Engine system and method for injector cut-out operation with improved exhaust heating

ABSTRACT

Various systems and methods are disclosed for carrying out combustion in a fuel-cut operation in some or all of the engine cylinders of a vehicle. Further, various subsystems are considered, such as fuel vapor purging, air-fuel ratio control, engine torque control, catalyst design, and exhaust system design.

[0001] The present application claims priority under 35 U.S.C. §120 to,and is a continuation-in-part, of U.S. application Ser. No. 10/064,014,titled “METHOD OF SPLIT IGNITION TIMING FOR IDLE SPEED CONTROL OF ANENGINE”, filed on Jun. 4, 2002, the entire contents of which isincorporated herein by reference in its entirety.

BACKGROUND AND SUMMARY

[0002] Engines are usually designed with the ability to deliver a peakoutput, although most engine operation is performed well below this peakvalue. As such, it can be beneficial to operate with some cylindersinducting air without fuel injection, since this can increase fueleconomy.

[0003] One approach to allow such operation in an engine is described inthe U.S. Pat. No. 4,467,602. In such a system, different catalysts canexperience different operating temperatures. As such, the approach in'602 uses a temperature sensor and provides rich engine operation tokeep maintain emission control. Further, the system in '602 the twoclosest catalysts to the engine are at different distances from theengine.

[0004] However, the inventors have recognized a disadvantage with theapproach described in '602. Specifically, during a cold engine start, itmay take one of the closer catalysts longer to reach its operatingtemperature.

[0005] This can be overcome by operating the cylinder groups coupled tocatalysts in different locations in a different way. For example, in oneexample, a method for controlling an engine with at least a first set ofcylinders and a second set of cylinders is provided. The methodcomprises:

[0006] during an engine start, operating the second set of cylinderswith an ignition timing more retarded than an ignition timing of saidfirst set of cylinders, and

[0007] during engine operation, operating the first set of cylinderswith injected fuel to carry out combustion and operating the second setof cylinders to induct air and without injected fuel.

[0008] In this way, it is possible to obtain the benefits of fuel cutoperation, while having the ability to provide good emission controlduring engine starting.

[0009] In another aspect, the inventors herein have recognized anotherdisadvantage with such the approach of '602. Specifically, suchoperation may maintain temperature of the catalysts, but overallemissions may still increase since the oxidation of rich gasses withlean gasses may be less efficient than operation about stoichiometry.

[0010] Another approach that could be used in such a system is to endfuel cut operation if catalyst temperature becomes too low and re-enablefuel cut cylinders to thereby provide stoichiometric operation beforecatalyst temperature drops.

[0011] However, the inventors herein have recognized a disadvantage withsuch an approach. Specifically, using temperature to prematurely endfuel cut operation can lead to less fuel economy improvement thatotherwise could be available. Yet, if fuel cut-operation is continuedbeyond this point, then emission may increase when re-enabling fuel cutcylinders since one of the catalysts may be below its light-offtemperature.

[0012] The above disadvantage can be overcome by an improved method torapidly heat a catalyst that is cooled during fuel cut operation. Forexample, a method for controlling an engine with at least a first set ofcylinders and a second set of cylinders, where a first catalyst iscoupled to the first set and a second catalyst is coupled to both saidfirst and second set downstream of said first catalyst, can be used. Themethod comprises:

[0013] operating the first set of cylinders with injected fuel to carryout combustion and operating the second set of cylinders to induct airand without injected fuel; and

[0014] after said operation, commencing fuel injection in said secondset of cylinders, and during said commencing, operating said second setof cylinders with an ignition timing that is more retarded than anignition timing of said first set, with said first set carrying outcombustion about stoichiometry.

[0015] In this way, it is possible to provide an exhaust gas mixtureabout stoichiometry to the second catalyst, and at the same time providemost of the heat to the second catalyst which can then rapidly reach itsoperating temperature. In this way emission can be reduced and fueleconomy improved by having the ability to extend fuel cut operation evenif temperature of a catalyst falls.

BRIEF DESCRIPTION OF THE FIGURES

[0016] The above features and advantages will be readily apparent fromthe following detailed description of example embodiment(s). Further,these features and advantages will also be apparent from the followingdrawings.

[0017]FIG. 1 is a block diagram of a vehicle illustrating variouscomponents of the powertrain system;

[0018]FIGS. 1A and 1B show a partial engine view;

[0019]FIGS. 2A-2T show various schematic system configurations;

[0020] FIGS. 3A1-3A2 are graphs representing different engine operatingmodes at different speed torque regions;

[0021]FIGS. 3B-3C, 4-5, 7-11, 12A-12B, 13A, 13C1-C2, and 16-20 and 34are high level flow charts showing example routines and methods;

[0022] FIGS. 6A-D, 13B1-13B2 and 13D1-13D2 are graphs show exampleoperation;

[0023]FIGS. 14 and 15 show a bifurcated catalyst;

[0024]FIG. 21 contains graphs showing a deceleration torque requestbeing clipped via a torque converter model to keep engine speed above aminimum allowed value;

[0025]FIGS. 22-27 show engine torque over an engine cycle during atransition between different cylinder cut-out modes;

[0026]FIGS. 28-33 show Fourier diagrams of engine torque excitationacross various frequencies for different operating modes, and whentransitioning between operating modes.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT(S) OF THE INVENTION

[0027] Referring to FIG. 1, internal combustion engine 10, furtherdescribed herein with particular reference to FIGS. 1A and 1B, is showncoupled to torque converter 11 via crankshaft 13. Torque converter 11 isalso coupled to transmission 15 via turbine shaft 17. Torque converter11 has a bypass, or lock-up clutch 14 which can be engaged, disengaged,or partially engaged. When the clutch is either disengaged or partiallyengaged, the torque converter is said to be in an unlocked state. Thelock-up clutch 14 can be actuated electrically, hydraulically, orelectro-hydraulically, for example. The lock-up clutch 14 receives acontrol signal (not shown) from the controller, described in more detailbelow. The control signal may be a pulse width modulated signal toengage, partially engage, and disengage, the clutch based on engine,vehicle, and/or transmission operating conditions. Turbine shaft 17 isalso known as transmission input shaft. Transmission 15 comprises anelectronically controlled transmission with a plurality of selectablediscrete gear ratios. Transmission 15 also comprises various othergears, such as, for example, a final drive ratio (not shown).Transmission 15 is also coupled to tire 19 via axle 21. Tire 19interfaces the vehicle (not shown) to the road 23. Note that in oneexample embodiment, this powertrain is coupled in a passenger vehiclethat travels on the road.

[0028]FIGS. 1A and 1B show one cylinder of a multi-cylinder engine, aswell as the intake and exhaust path connected to that cylinder. Asdescribed later herein with particular reference to FIG. 2, there arevarious configurations of the cylinders and exhaust system, as well asvarious configuration for the fuel vapor purging system and exhaust gasoxygen sensor locations.

[0029] Continuing with FIG. 1A, direct injection spark ignited internalcombustion engine 10, comprising a plurality of combustion chambers, iscontrolled by electronic engine controller 12. Combustion chamber 30 ofengine 10 is shown including combustion chamber walls 32 with piston 36positioned therein and connected to crankshaft 40. A starter motor (notshown) is coupled to crankshaft 40 via a flywheel (not shown). In thisparticular example, piston 36 includes a recess or bowl (not shown) tohelp in forming stratified charges of air and fuel. Combustion chamber,or cylinder, 30 is shown communicating with intake manifold 44 andexhaust manifold 48 via respective intake valves 52 a and 52 b (notshown), and exhaust valves 54 a and 54 b (not shown). Fuel injector 66Ais shown directly coupled to combustion chamber 30 for deliveringinjected fuel directly therein in proportion to the pulse width ofsignal fpw received from controller 12 via conventional electronicdriver 68. Fuel is delivered to fuel injector 66A by a conventional highpressure fuel system (not shown) including a fuel tank, fuel pumps, anda fuel rail.

[0030] Intake manifold 44 is shown communicating with throttle body 58via throttle plate 62. In this particular example, throttle plate 62 iscoupled to electric motor 94 so that the position of throttle plate 62is controlled by controller 12 via electric motor 94. This configurationis commonly referred to as electronic throttle control (ETC), which isalso utilized during idle speed control. In an alternative embodiment(not shown), which is well known to those skilled in the art, a bypassair passageway is arranged in parallel with throttle plate 62 to controlinducted airflow during idle speed control via a throttle control valvepositioned within the air passageway.

[0031] Exhaust gas sensor 76 is shown coupled to exhaust manifold 48upstream of catalytic converter 70 (note that sensor 76 corresponds tovarious different sensors, depending on the exhaust configuration asdescribed below with regard to FIG. 2. Sensor 76 may be any of manyknown sensors for providing an indication of exhaust gas air/fuel ratiosuch as a linear oxygen sensor, a UEGO, a two-state oxygen sensor, anEGO, a HEGO, or an HC or CO sensor. In this particular example, sensor76 is a two-state oxygen sensor that provides signal EGO to controller12 which converts signal EGO into two-state signal EGOS. A high voltagestate of signal EGOS indicates exhaust gases are rich of stoichiometryand a low voltage state of signal EGOS indicates exhaust gases are leanof stoichiometry. Signal EGOS is used to advantage during feedbackair/fuel control in a conventional manner to maintain average air/fuelat stoichiometry during the stoichiometric homogeneous mode ofoperation.

[0032] Conventional distributorless ignition system 88 provides ignitionspark to combustion chamber 30 via spark plug 92 in response to sparkadvance signal SA from controller 12.

[0033] Controller 12 causes combustion chamber 30 to operate in either ahomogeneous air/fuel mode or a stratified air/fuel mode by controllinginjection timing. In the stratified mode, controller 12 activates fuelinjector 66A during the engine compression stroke so that fuel issprayed directly into the bowl of piston 36. Stratified air/fuel layersare thereby formed. The strata closest to the spark plug contain astoichiometric mixture or a mixture slightly rich of stoichiometry, andsubsequent strata contain progressively leaner mixtures. During thehomogeneous mode, controller 12 activates fuel injector 66A during theintake stroke so that a substantially homogeneous air/fuel mixture isformed when ignition power is supplied to spark plug 92 by ignitionsystem 88. Controller 12 controls the amount of fuel delivered by fuelinjector 66A so that the homogeneous air/fuel mixture in chamber 30 canbe selected to be at stoichiometry, a value rich of stoichiometry, or avalue lean of stoichiometry. The stratified air/fuel mixture will alwaysbe at a value lean of stoichiometry, the exact air/fuel being a functionof the amount of fuel delivered to combustion chamber 30. An additionalsplit mode of operation wherein additional fuel is injected during theexhaust stroke while operating in the stratified mode is also possible.

[0034] Nitrogen oxide (NOx) adsorbent or trap 72 is shown positioneddownstream of catalytic converter 70. NOx trap 72 is a three-waycatalyst that adsorbs NOx when engine 10 is operating lean ofstoichiometry. The adsorbed NOx is subsequently reacted with HC and COand catalyzed when controller 12 causes engine 10 to operate in either arich homogeneous mode or a near stoichiometric homogeneous mode suchoperation occurs during a NOx purge cycle when it is desired to purgestored NOx from NOx trap 72, or during a vapor purge cycle to recoverfuel vapors from fuel tank 160 and fuel vapor storage canister 164 viapurge control valve 168, or during operating modes requiring more enginepower, or during operation modes regulating temperature of the omissioncontrol devices such as catalyst 70 or NOx trap 72. (Again, note thatemission control devices 70 and 72 can correspond to various devicesdescribed in FIGS. 2A-R). Also note that various types of purgingsystems can be used, as described in more detail below with regard toFIGS. 2A-R.

[0035] Controller 12 is shown in FIG. 1A as a conventionalmicrocomputer, including microprocessor unit 102, input/output ports104, an electronic storage medium for executable programs andcalibration values shown as read only memory chip 106 in this particularexample, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 100 coupled to throttle body 58; enginecoolant temperature (ECT) from temperature sensor 112 coupled to coolingsleeve 114; a profile ignition pickup signal (PIP) from Hall effectsensor 118 coupled to crankshaft 40; and throttle position TP fromthrottle position sensor 120; and absolute Manifold Pressure Signal MAPfrom sensor 122. Engine speed signal RPM is generated by controller 12from signal PIP in a conventional manner and manifold pressure signalMAP from a manifold pressure sensor provides an indication of vacuum, orpressure, in the intake manifold. During stoichiometric operation, thissensor can give and indication of engine load. Further, this sensor,along with engine speed, can provide an estimate of charge (includingair) inducted into the cylinder. In a one example, sensor 118, which isalso used as an engine speed sensor, produces a predetermined number ofequally spaced pulses every revolution of the crankshaft.

[0036] In this particular example, temperature Tcat1 of catalyticconverter 70 and temperature Tcat2 of emission control device 72 (whichcan be a NOx trap) are inferred from engine operation as disclosed inU.S. Pat. No. 5,414,994, the specification of which is incorporatedherein by reference. In an alternate embodiment, temperature Tcat1 isprovided by temperature sensor 124 and temperature Tcat2 is provided bytemperature sensor 126.

[0037] Continuing with FIG. 1A, camshaft 130 of engine 10 is showncommunicating with rocker arms 132 and 134 for actuating intake valves52 a, 52 b and exhaust valve 54 a. 54 b. Camshaft 130 is directlycoupled to housing 136. Housing 136 forms a toothed wheel having aplurality of teeth 138. Housing 136 is hydraulically coupled to an innershaft (not shown), which is in turn directly linked to camshaft 130 viaa timing chain (not shown). Therefore, housing 136 and camshaft 130rotate at a speed substantially equivalent to the inner camshaft. Theinner camshaft rotates at a constant speed ratio to crankshaft 40.However, by manipulation of the hydraulic coupling as will be describedlater herein, the relative position of camshaft 130 to crankshaft 40 canbe varied by hydraulic pressures in advance chamber 142 and retardchamber 144. By allowing high pressure hydraulic fluid to enter advancechamber 142, the relative relationship between camshaft 130 andcrankshaft 40 is advanced. Thus, intake valves 52 a, 52 b and exhaustvalves 54 a, 54 b open and close at a time earlier than normal relativeto crankshaft 40. Similarly, by allowing high pressure hydraulic fluidto enter retard chamber 144, the relative relationship between camshaft130 and crankshaft 40 is retarded. Thus, intake valves 52 a, 52 b, andexhaust valves 54 a, 54 b open and close at a time later than normalrelative to crankshaft 40.

[0038] Teeth 138, being coupled to housing 136 and camshaft 130, allowfor measurement of relative cam position via cam timing sensor 150providing signal VCT to controller 12. Teeth 1, 2, 3, and 4 arepreferably used for measurement of cam timing and are equally spaced(for example, in a V-8 dual bank engine, spaced 90 degrees apart fromone another) while tooth 5 is preferably used for cylinderidentification, as described later herein. In addition, controller 12sends control signals (LACT, RACT) to conventional solenoid valves (notshown) to control the flow of hydraulic fluid either into advancechamber 142, retard chamber 144, or neither.

[0039] Relative cam timing is measured using the method described inU.S. Pat. No. 5,548,995, which is incorporated herein by reference. Ingeneral terms, the time, or rotation angle between the rising edge ofthe PIP signal and receiving a signal from one of the plurality of teeth138 on housing 136 gives a measure of the relative cam timing. For theparticular example of a V-8 engine, with two cylinder banks and afive-toothed wheel, a measure of cam timing for a particular bank isreceived four times per revolution, with the extra signal used forcylinder identification.

[0040] Sensor 160 provides an indication of both oxygen concentration inthe exhaust gas as well as NOx concentration. Signal 162 providescontroller a voltage indicative of the O2 concentration while signal 164provides a voltage indicative of NOx concentration. Alternatively,sensor 160 can be a HEGO, UEGO, EGO, or other type of exhaust gassensor. Also note that, as described above with regard to sensor 76,sensor 160 can correspond to various different sensors depending on thesystem configuration, as described in more detail below with regard toFIG. 2.

[0041] As described above, FIGS. 1A (and 1B) merely show one cylinder ofa multi-cylinder engine, and that each cylinder has its own set ofintake/exhaust valves, fuel injectors, spark plugs, etc.

[0042] Referring now to FIG. 1B, a port fuel injection configuration isshown where fuel injector 66B is coupled to intake manifold 44, ratherthan directly cylinder 30.

[0043] Also, in the example embodiments described herein, the engine iscoupled to a starter motor (not shown) for starting the engine. Thestarter motor is powered when the driver turns a key in the ignitionswitch on the steering column, for example. The starter is disengagedafter engine start as evidence, for example, by engine 10 reaching apredetermined speed after a predetermined time. Further, in thedisclosed embodiments, an exhaust gas recirculation (EGR) system routesa desired portion of exhaust gas from exhaust manifold 48 to intakemanifold 44 via an EGR valve (not shown). Alternatively, a portion ofcombustion gases may be retained in the combustion chambers bycontrolling exhaust valve timing.

[0044] The engine 10 operates in various modes, including leanoperation, rich operation, and “near stoichiometric” operation. “Nearstoichiometric” operation refers to oscillatory operation around thestoichiometric air fuel ratio. Typically, this oscillatory operation isgoverned by feedback from exhaust gas oxygen sensors. In this nearstoichiometric operating mode, the engine is operated withinapproximately one air-fuel ratio of the stoichiometric air-fuel ratio.This oscillatory operation is typically on the order of 1 Hz, but canvary faster and slower than 1 Hz. Further, the amplitude of theoscillations are typically within 1 a/f ratio of stoichiometry, but canbe greater than 1 a/f ratio under various operating conditions. Notethat this oscillation does not have to be symmetrical in amplitude ortime. Further note that an air-fuel bias can be included, where the biasis adjusted slightly lean, or rich, of stoichiometry (e.g., within 1 a/fratio of stoichiometry). Also note that this bias and the lean and richoscillations can be governed by an estimate of the amount of oxygenstored in upstream and/or downstream three way catalysts.

[0045] As described below, feedback air-fuel ratio control is used forproviding the near stoichiometric operation. Further, feedback fromexhaust gas oxygen sensors can be used for controlling air-fuel ratioduring lean and during rich operation. In particular, a switching type,heated exhaust gas oxygen sensor (HEGO) can be used for stoichiometricair-fuel ratio control by controlling fuel injected (or additional airvia throttle or VCT) based on feedback from the HEGO sensor and thedesired air-fuel ratio. Further, a UEGO sensor (which provides asubstantially linear output versus exhaust air-fuel ratio) can be usedfor controlling air-fuel ratio during lean, rich, and stoichiometricoperation. In this case, fuel injection (or additional air via throttleor VCT) is adjusted based on a desired air-fuel ratio and the air-fuelratio from the sensor. Further still, individual cylinder air-fuel ratiocontrol could be used, if desired.

[0046] Also note that various methods can be used to maintain thedesired torque such as, for example, adjusting ignition timing, throttleposition, variable cam timing position, exhaust gas recirculationamount, and a number of cylinders carrying out combustion. Further,these variables can be individually adjusted for each cylinder tomaintain cylinder balance among all the cylinder groups.

[0047] Referring now to FIG. 2A, a first example configuration isdescribed using a V-8 engine, although this is simply one example, sincea V-10, V-12, 14, 16, etc., could also be used. Note that while numerousexhaust gas oxygen sensors are shown, a subset of these sensors can alsobe used. Further, only a subset of the emission control devices can beused, and a non-y-pipe configuration can also be used. As shown in FIG.2A, some cylinders of first combustion chamber group 210 are coupled tothe first catalytic converter 220, while the remainder are coupled tocatalyst 222. Upstream of catalyst 220 and downstream of the firstcylinder group 210 is an exhaust gas oxygen sensor 230. Downstream ofcatalyst 220 is a second exhaust gas sensor 232. In this example, groups210 and 212 each have four cylinders. However, either group 210 or group212 could be divided into other groups, such as per cylinder bank. Thiswould provide four cylinder groups (two on each bank, each with twocylinders in the group). In this way, two different cylinder groups canbe coupled to the same exhaust gas path on one side of the engine'sbank.

[0048] Similarly, some cylinders of second combustion chamber group 212are coupled to a second catalyst 222, while the remainder are coupled tocatalyst 220. Upstream and downstream are exhaust gas oxygen sensors 234and 236 respectively. Exhaust gas spilled from the first and secondcatalyst 220 and 222 merge in a Y-pipe configuration before enteringdownstream under body catalyst 224. Also, exhaust gas oxygen sensors 238and 240 are positioned upstream and downstream of catalyst 224,respectively.

[0049] In one example embodiment, catalysts 220 and 222 are platinum andrhodium catalysts that retain oxidants when operating lean and releaseand reduce the retained oxidants when operating rich. Further, thesecatalysts can have multiple bricks, and further these catalysts canrepresent several separate emission control devices.

[0050] Similarly, downstream underbody catalyst 224 also operates toretain oxidants when operating lean and release and reduce retainedoxidants when operating rich. As described above, downstream catalyst224 can be a group of bricks, or several emission control devices.Downstream catalyst 224 is typically a catalyst including a preciousmetal and alkaline earth and alkaline metal and base metal oxide. Inthis particular example, downstream catalyst 224 contains platinum andbarium.

[0051] Note that various other emission control devices could be used,such as catalysts containing palladium or perovskites. Also, exhaust gasoxygen sensors 230 to 240 can be sensors of various types. For example,they can be linear oxygen sensors for providing an indication ofair-fuel ratio across a broad range. Also, they can be switching typeexhaust gas oxygen sensors that provide a switch in sensor output at thestoichiometric point. Also, the system can provide less than all ofsensors 230 to 240, for example, only sensors 230, 234, and 240. Inanother example, only sensor 230, 234 are used with only devices 220 and222. Also, while FIG. 2A shows a V-8 engine, various other numbers ofcylinders could be used. For example, an I4 engine can be used, wherethere are two groups of two cylinders leading to a common exhaust pathwith and upstream and downstream emission control device.

[0052] When the system of FIG. 2A is operated in an AIR/LEAN mode, firstcombustion group 210 is operated at a lean air-fuel ratio (typicallyleaner than about 18:1) and second combustion group 212 is operatedwithout fuel injection. Thus, in this case, and during this operation,the exhaust air-fuel ratio is a mixture of air from the cylinderswithout injected fuel, and a lean air fuel ratio from the cylinderscombusting a lean air-fuel mixture. In this way, fuel vapors from valve168 can be burned in group 210 cylinders even during the AIR/LEAN mode.Note that the engine can also operate in any of the 5 various modesdescribed below with regard to FIG. 3A1, for example. Note that, asdescribed in more detail below, the mode selected may be based ondesired engine output torque, whether idle speed control is active,exhaust temperature, and various other operating conditions.

[0053] Referring now to FIG. 2B, a system similar to that in FIG. 2A isshown, however a dual fuel vapor purge system is shown with first andsecond purge valves 168A and 168B. Thus, independent control of fuelvapors between each of groups 210 and 212 is provided. When the systemof FIG. 2B is operated in an AIR/LEAN mode, first combustion group 210is operated at a lean air-fuel ratio (typically leaner than about 18:1),second combustion group 212 is operated without fuel injection, and fuelvapor purging can be enabled to group 210 via valve 168A (and disabledto group 212 via valve 168B). Alternatively, first combustion group 210is operated without fuel injection, second combustion group 212 isoperated at a lean air-fuel ratio, and fuel vapor purging can be enabledto group 212 via valve 168B (and disabled to group 210 via valve 168A).In this way, the system can perform the AIR/LEAN mode in differentcylinder groups depending on operating conditions, or switch between thecylinder groups to provide even wear, etc.

[0054] Referring now to FIG. 2C, a V-6 engine is shown with first group250 on one bank, and second group 252 on a second bank. The remainder ofthe exhaust system is similar to that described above in FIGS. 2A and2B. The fuel vapor purge system has a single control valve 168 fed tocylinders in group 250.

[0055] When the system of FIG. 2C is operated in an AIR/LEAN mode, firstcombustion group 250 is operated at a lean air-fuel ratio (typicallyleaner than about 18:1) and second combustion group 252 is operatedwithout fuel injection. Thus, in this case, and during this operation,the exhaust air-fuel ratio is a mixture of air from the cylinderswithout injected fuel, and a lean air fuel ratio from the cylinderscombusting a lean air-fuel mixture. In this way, fuel vapors from valve168 can be burned in group 250 cylinders even during the AIR/LEAN mode.Note that the engine can also operate in any of the 5 various modesdescribed below with regard to FIG. 3A1, for example.

[0056] Referring now to FIG. 2D, a system similar to that in FIG. 2C isshown, however a dual fuel vapor purge system is shown with first andsecond purge valves 168A and 168B. Thus, independent control of fuelvapors between each of groups 250 and 252 is provided. When the systemof FIG. 2D is operated in an AIR/LEAN mode, first combustion group 250is operated at a lean air-fuel ratio (typically leaner than about 18:1),second combustion group 252 is operated without fuel injection, and fuelvapor purging can be enabled to group 250 via valve 168A (and disabledto group 212 via valve 168B). Alternatively, first combustion group 250,is operated without fuel injection, second combustion group 252 isoperated at a lean air-fuel ratio, and fuel vapor purging can be enabledto group 252 via valve 168B (and disabled to group 250 via valve 168A).In this way, the system can perform the AIR/LEAN mode in differentcylinder groups depending on operating conditions, or switch between thecylinder groups to provide even wear, etc. Note that the engine can alsooperate in any of the 5 various modes described below with regard toFIG. 3A1, for example.

[0057] Referring now to FIG. 2E, a V-6 engine is shown similar to thatof FIG. 2C, with the addition of an exhaust gas recirculation (EGR)system and valve 178. As illustrated in FIG. 2E, the EGR system takesexhaust gasses exhausted from cylinders in cylinder group 250 to be fedto the intake manifold (downstream of the throttle). The EGR gasses thenpass to both cylinder groups 250 and 252 via the intake manifold. Theremainder of the exhaust system is similar to that described above inFIGS. 2A and 2B. Note that, as above, the engine can also operate in anyof the 5 various modes described below with regard to FIG. 3A1, forexample.

[0058] Referring now to FIG. 2F, a system similar to that in FIG. 2E isshown, however a dual fuel vapor purge system is shown with first andsecond purge valves 168A and 168B. Further, EGR gasses are taken fromgroup 252, rather than 250. Again, the engine can also operate in any ofthe 5 various modes described below with regard to FIG. 3A1, forexample.

[0059] Referring now to FIG. 2G, a system similar to that in FIG. 2A isshown, however an exhaust gas recirculation system and valve 178 isshown for introducing exhaust gasses that are from some cylinders ingroup 210 and some cylinders in group 212 into the intake manifolddownstream of the throttle valve. Again, the engine can also operate inany of the 5 various modes described below with regard to FIG. 3A1, forexample.

[0060] Referring now to FIG. 2H, a system similar to that in FIG. 2G isshown, however a dual fuel vapor purge system is shown with first andsecond purge valves 168A and 168B. Again, the engine can also operate inany of the 5 various modes described below with regard to FIG. 3A1, forexample.

[0061] Referring now to FIG. 2I, a V-6 engine is shown with firstcylinder group 250 on a first bank, and second cylinder group 252 on asecond bank. Further, a first exhaust path is shown coupled to group 250including an upstream emission control device 220 and a downstreamemission control device 226. Further, an exhaust manifold sensor 230, anintermediate sensor 232 between devices 220 and 226, and a downstreamsensor 239 are shown for measuring various exhaust gas air-fuel ratiovalues. In one example, devices 220 and 226 are three way catalystshaving one or more bricks enclosed therein. Similarly, a second exhaustpath is shown coupled to group 252 including an upstream emissioncontrol device 222 and a downstream emission control device 228.Further, an exhaust manifold sensor 234, an intermediate sensor 236between devices 222 and 228, and a downstream sensor 241 are shown formeasuring various exhaust gas air-fuel ratio values. In one example,devices 222 and 228 are three way catalysts having one or more bricksenclosed therein.

[0062] Continuing with FIG. 2I, both groups 250 and 252 have a variablevalve actuator (270 and 272, respectively) coupled thereto to adjustoperation of the cylinder intake and/or exhaust valves. In one example,these are variable cam timing actuators as described above in FIGS. 1Aand 1B. However, alternative actuators can be used, such as variablevalve lift, or switching cam systems. Further, individual actuators canbe coupled to each cylinder, such as with electronic valve actuatorsystems.

[0063] Note that FIG. 2I, as well as the rest of the figures in FIG. 2are schematic representations. For example, the purge vapors from valve168 can be delivered via intake ports with inducted air as in FIG. 2J,rather than via individual paths to each cylinder in the group as inFIG. 2I. And as before, the engine can also operate in various enginemodes, such as in FIG. 3A1, or as in the various routines describedbelow herein.

[0064] Referring now to FIG. 2J, a system similar to that of FIG. 2I isshown with an alternative fuel vapor purge delivery to the intakemanifold, which delivery fuel vapors from valve 168. Note that such asystem can be adapted for various systems described in FIG. 2 above andbelow, as mentioned with regard to FIG. 2I, although one approach mayprovide advantages over the other depending on the operating modes ofinterest.

[0065] Referring now to FIG. 2K, a V-8 engine is shown with a firstgroup of cylinders 210 spanning both cylinder banks, and a second groupof cylinders 212 spanning both cylinder banks. Further, an exhaustsystem configuration is shown which brings exhaust gasses from the group212 together before entering an emission control device 260. Likewise,the gasses exhausted from device 260 are mixed with untreated exhaustgasses from group 210 before entering emission control device 262. Thisis accomplished, in this example, via a cross-over type exhaustmanifold. Specifically, exhaust manifold 256 is shown coupled to theinner two cylinders of the top bank of group 212; exhaust manifold 257is shown coupled to the outer two cylinders of the top bank of group210; exhaust manifold 258 is shown coupled to the inner two cylinders ofthe bottom bank of group 210; and exhaust manifold 259 is shown coupledto the outer two cylinders of the bottom bank of group 212. Then,manifolds 257 and 258 are fed together and then fed to mix with gassesexhausted from device 250 (before entering device 262), and manifolds256 and 259 are fed together and fed to device 260. Exhaust gas air-fuelsensor 271 is located upstream of device 260 (after manifolds 256 and259 join). Exhaust gas air-fuel sensor 273 is located upstream of device262 before the gasses from the group 210 join 212. Exhaust gas air-fuelsensor 274 is located upstream of device 262 after the gasses from thegroup 210 join 212. Exhaust gas air-fuel sensor 276 is locateddownstream of device 276.

[0066] In one particular example, devices 260 and 262 are three waycatalysts, and when the engine operates in a partial fuel cut operation,group 212 carries out combustion oscillating around stoichiometry(treated in device 260), while group 210 pumps are without injectedfuel. In this case, device 262 is saturated with oxygen. Alternatively,when both cylinder groups are combusting, both devices 260 and 262 canoperate to treat exhausted emissions with combustion aboutstoichiometry. In this way, partial cylinder cut operation can beperformed in an odd fire V-8 engine with reduced noise and vibration.

[0067] Note that there can also be additional emission control devices(not shown), coupled exclusively to group 210 upstream of device 262.

[0068] Referring now to FIG. 2L, another V-8 engine is shown with afirst group of cylinders 210 spanning both cylinder banks, and a secondgroup of cylinders 212 spanning both cylinder banks. However, in thisexample, a first emission control device 280 is coupled to two cylindersin the top bank (from group 212) and a second emission control device282 is coupled to two cylinders of the bottom bank (from group 212).Downstream of device 280, manifold 257 joins exhaust gasses from theremaining two cylinders in the top bank (from group 210). Likewise,downstream of device 282, manifold 258 joins exhaust gasses from theremaining two cylinders in the bottom bank (from group 210). Then, thesetwo gas streams are combined before entering downstream device 284.

[0069] In one particular example, devices 280, 282, and 284 are threeway catalysts, and when the engine operates in a partial fuel cutoperation, group 212 carries out combustion oscillating aroundstoichiometry (treated in devices 280 and 282), while group 210 pumpsare without injected fuel. In this case, device 284 is saturated withoxygen. Alternatively, when both cylinder groups are combusting, devices280, 282, and 284 can operate to treat exhausted emissions withcombustion about stoichiometry. In this way, partial cylinder cutoperation can be performed in an odd fire V-8 engine with reduced noiseand vibration.

[0070] Note that both FIGS. 2K and 2L shows a fuel vapor purge systemand valve 168 for delivering fuel vapors to group 210.

[0071] Referring now to FIG. 2M, two banks of a V8 engine are shown. Theodd fire V8 engine is operated by, in each bank, running two cylindersabout stoichiometry and two cylinders with air. The stoichiometric andair exhausts are then directed through a bifurcated exhaust pipe to abifurcated metal substrate catalyst, described in more detail below withregard to FIGS. 14 and 15. The stoichiometric side of the catalystreduces the emissions without the interference from the air side of theexhaust. The heat from the stoichiometric side of the exhaust keeps thewhole catalyst above a light-off temperature during operatingconditions. When the engine is then operated in 8-cylinder mode, the airside of the catalyst is in light-off condition and can reduce theemissions. A rich regeneration of the air side catalyst can also beperformed when changing from 4 to 8 cylinder mode whereby the 2cylinders that were running air would be momentarily operated rich toreduce the oxygen storage material in the catalyst prior to returning tostoichiometric operation, as discussed in more detail below. Thisregeneration can achieve 2 purposes: 1) the catalyst will function in3-way operation when the cylinders are brought back to stoichiometricoperation and 2) the regeneration of the oxygen storage material willresult in the combustion of the excess CO/H2 in the rich exhaust andwill raise the temperature of the catalyst if it has cooled duringperiod when only air was pumped through the deactivated cylinders

[0072] Continuing with FIG. 2M, exhaust manifold 302 is shown coupled tothe inner two cylinders of the top bank (from group 212). Exhaustmanifold 304 is shown coupled to the outer two cylinders of the top bank(from group 210). Exhaust manifold 308 is shown coupled to the inner twocylinders of the bottom bank (from group 210). Exhaust manifold 306 isshown coupled to the outer two cylinders of the bottom bank (from group212). Exhaust manifolds 302 and 304 are shown leading to an inlet pipe(305) of device 300. Likewise, exhaust manifolds 306 and 308 are shownleading to an inlet pipe (307) of device 302, which, as indicated above,are described in more detail below. The exhaust gasses from devices 300and 302 are mixed individually and then combined before entering device295. Further, a fuel vapor purge system and control valve 168 are showndelivering fuel vapors to group 212.

[0073] Again, as discussed above, an I-4 engine could also be used,where the engine has a similar exhaust and inlet configuration to onebank of the V-8 engine configurations shown above and below in thevarious Figures.

[0074]FIGS. 2N, 20, and 2P are similar to FIGS. 2K, 2L, and 2M,respectively, except for the addition of a first and second variablevalve actuation units, in this particular example, variable cam timingactuators 270 and 272.

[0075] Referring now to FIG. 2Q, an example V-6 engine is shown withemission control devices 222 and 224. In this example, there is noemission control device coupled exclusively to group 250. A thirdemission control device (not shown) can be added downstream. Also, FIG.2Q shows an example V-6 engine, however, others can be used in thisconfiguration, such as a V-10, V-12, etc.

[0076] Referring now to FIG. 2R, an example system is shown where fuelvapors are passed to all of the cylinders, and in the case of cylinderfuel cut operation, fuel vapor purging operating is suspended.

[0077] Referring now to FIGS. 2S and 2T, still another example system isshown for an engine with variable valve operation (such as variable camtiming from devices 270 and 272), along with a fuel vapor purging systemhaving a single valve 168 in 2S, and dual purge valves 168A, B in 2T.

[0078] There are various fuel vapor modes for FIGS. 2A-2T, some of whichare listed below:

[0079] operate the first group of cylinders lean with fuel vapor purge(and injected fuel), and the other group inducting gasses withoutinjected fuel

[0080] operate the first group of cylinders stoichiometric with fuelvapor purge (and injected fuel), and the other group inducting gasseswithout injected fuel

[0081] operate the first group of cylinders rich with fuel vapor purge(and injected fuel), and the other group inducting gasses withoutinjected fuel

[0082] operate the first group of cylinders lean with fuel vapor purge(and injected fuel), and the other group stoichiometric without fuelvapors

[0083] operate the first group of cylinders stoichiometric with fuelvapor purge (and injected fuel), and the other group stoichiometricwithout fuel vapors

[0084] operate the first group of cylinders rich with fuel vapor purge(and injected fuel), and the other group stoichiometric without fuelvapors

[0085] operate the first group of cylinders lean with fuel vapor purge(and injected fuel), and the other group lean without fuel vapors

[0086] operate the first group of cylinders stoichiometric with fuelvapor purge (and injected fuel), and the other group lean without fuelvapors

[0087] operate the first group of cylinders rich with fuel vapor purge(and injected fuel), and the other group lean without fuel vapors

[0088] operate the first group of cylinders lean with fuel vapor purge(and injected fuel), and the other group rich without fuel vapors

[0089] operate the first group of cylinders stoichiometric with fuelvapor purge (and injected fuel), and the other group rich without fuelvapors

[0090] operate the first group of cylinders rich with fuel vapor purge(and injected fuel), and the other group rich without fuel vapors

[0091] operate the first group of cylinders lean with fuel vapor purge(and injected fuel), and the other group rich with fuel vapors (andinjected fuel)

[0092] operate the first group of cylinders stoichiometric with fuelvapor purge (and injected fuel), and the other group rich with fuelvapors (and injected fuel)

[0093] operate the first group of cylinders rich with fuel vapor purge(and injected fuel), and the other group rich with fuel vapors (andinjected fuel)

[0094] operate the first group of cylinders lean with fuel vapor purge(and injected fuel), and the other group lean with fuel vapors (andinjected fuel)

[0095] operate the first group of cylinders stoichiometric with fuelvapor purge (and injected fuel), and the other group lean with fuelvapors (and injected fuel)

[0096] operate the first group of cylinders rich with fuel vapor purge(and injected fuel), and the other group lean with fuel vapors (andinjected fuel)

[0097] operate the first group of cylinders lean with fuel vapor purge(and injected fuel), and the other group stoichiometric with fuel vapors(and injected fuel)

[0098] operate the first group of cylinders stoichiometric with fuelvapor purge (and injected fuel), and the other group stoichiometric withfuel vapors (and injected fuel)

[0099] operate the first group of cylinders rich with fuel vapor purge(and injected fuel), and the other group stoichiometric with fuel vapors(and injected fuel)

[0100] Each of these modes can include further variation, such asdifferent VCT timing between cylinder banks, etc. Also note thatoperation at a cylinder cut condition provides a practically infiniteair-fuel ratio, since substantially no fuel is being injected by thefuel injectors for that cylinder (although there may be some fuelpresent due to fuel around the intake valves and in the intake port thatwill eventually decay away). As such, the effective air-fuel ratio issubstantially greater than about 100:1, for example. Although, dependingon the engine configuration, it could vary between 60:1 to practicallyan infinite value.

[0101] Regarding the various systems shown in FIGS. 2A-R, differentsystem configurations can present their own challenges that areaddressed herein. For example, V-8 engines, such as in FIG. 2A, forexample, can have uneven firing order, so that if it is desired todisable a group of 4 cylinders, then two cylinders on each bank aredisabled to provide acceptable vibration. However, this presentschallenges since, as shown in FIG. 2A, some exhaust systemconfigurations treat emissions from the entire bank together. Further,as shown in FIGS. 2S-2T, a single valve actuator can be used to adjustall of the valves of cylinders in a bank, even though some cylinders inthe bank are disabled, while others are operating. Unlike such V-8engines, some V-6 engines can be operated with a cylinder bank disabled,thus allowing an entire cylinder bank to be a group of cylinders thatare operated without fuel injection. Each of these different types ofsystems therefore has its own potential issues and challenges, as wellas advantages, as discussed and addressed by the routines described inmore detail below.

[0102] Note a bifurcated induction system (along firing order groups)can also be used for the fresh air. Such a system would be similar tothe system of FIG. 2T, except that the valves 168A and 168B would bereplaced by electronically controlled throttles. In this way, fuel vaporpurge could be fed to these two bifurcated induction systems, along withairflow, so that separate control of fuel vapor purge and airflow couldbe achieved between groups 210 and 212. However, as discussed above withregard to FIGS. 2I and 2J, for example, the VCT actuators can be used toobtain differing airflows (or air charges) between the cylinders ofgroups 250 and 252, without requiring a split induction system.

[0103] Several control strategies may be used to take advantage of theability to provide differing air amounts to differing cylinder groups,as discussed in more detail below. As one example, separate control ofairflow to different cylinder groups (e.g., via VCT actuators 270 and272 in FIGS. 2I and 2J), can be used in split ignition operation toallow more (or less) air flow into a group of cylinders. Also, undersome conditions there may be no one air amount that satisfiesrequirements of combustion stability, heat generation, and netpower/torque. For example, the power producing cylinder group may have aminimum spark advance for stability, or the heat producing cylindergroup may have a maximum heat flux due to material constraints. Bank-VCTand/or bifurcated intake could be used to achieve these requirementswith different air amounts selected for different cylinder groups.

[0104] Another control strategy example utilizing a bifurcating inlet(or using VCT in a V6 or V10) would allow lower pumping losses incylinder cut-out mode by changing the air flow to that group, where VCTis not solely associated with a firing group.

[0105] Further details of control routines are included below which canbe used with various engine configurations, such as the those describedin FIGS. 2A-2T. As will be appreciated by one of ordinary skill in theart, the specific routines described below in the flowcharts mayrepresent one or more of any number of processing strategies such asevent-driven, interrupt-driven, multi-tasking, multi-threading, and thelike. As such, various steps or functions illustrated may be performedin the sequence illustrated, in parallel, or in some cases omitted.Likewise, the order of processing is not necessarily required to achievethe features and advantages of the example embodiments of the inventiondescribed herein, but is provided for ease of illustration anddescription. Although not explicitly illustrated, one of ordinary skillin the art will recognize that one or more of the illustrated steps orfunctions may be repeatedly performed depending on the particularstrategy being used. Further, these figures graphically represent codeto be programmed into the computer readable storage medium in controller12.

[0106] Referring now to FIG. 3A1, a graph is shown illustrating engineoutput versus engine speed. In this particular description, engineoutput is indicated by engine torque, but various other parameters couldbe used, such as, for example: wheel torque, engine power, engine load,or others. The graph shows the maximum available torque that can beproduced in each of five operating modes. Note that a percentage ofavailable torque, or other suitable parameters, could be used in placeof maximum available torque. Further note that the horizontal line doesnot necessarily correspond to zero engine brake torque. The fiveoperating modes in this embodiment include:

[0107] Operating all cylinders with air pumping through andsubstantially no injected fuel (note: the throttle can be substantiallyopen, or closed, during this mode), illustrated as line 3A1-8 in theexample presented in FIG. 3A1;

[0108] Operating some cylinders lean of stoichiometry and remainingcylinders with air pumping through and substantially no injected fuel(note: the throttle can be substantially open during this mode),illustrated as line 33 ba in the example presented in FIG. 3A1;

[0109] Operating some cylinders at stoichiometry, and the remainingcylinders pumping air with substantially no injected fuel (note: thethrottle can be substantially open during this mode), shown as line3A1-4 in the example presented in FIG. 3A1;

[0110] Operating all cylinders lean of stoichiometry (note: the throttlecan be substantially open during this mode, shown as line 3A1-2 in theexample presented in FIG. 3A1;

[0111] Operating all cylinders substantially at stoichiometry (orslightly rich of stoichiometry) for maximum available engine torque,shown as line 3A1-0 in the example presented in FIG. 3A1.

[0112] Described above is one exemplary embodiment where an 8-cylinderengine is used and the cylinder groups are broken into two equal groups.However, various other configurations can be used, as discussed aboveand below. In particular, engines of various cylinder numbers can beused, and the cylinder groups can be broken down into unequal groups aswell as further broken down to allow for additional operating modes. Forthe example presented in FIG. 3A1 in which a V-8 engine is used, lines3A1-16 shows operation with 4 cylinders operating with air andsubstantially no fuel, line 3A1-14 shows operation with four cylindersoperating at stoichiometry and four cylinders operating with air, line3A1-12 shows 8 cylinders operating lean, line 3A1-10 shows 8 cylindersoperating at stoichiometry, and line 3A1-18 shows all cylindersoperating without injected fuel.

[0113] The above described graph illustrates the range of availabletorques in each of the described modes. In particular, for any of thedescribed modes, the available engine output torque can be any torqueless than the maximum amount illustrated by the graph. Also note that inany mode where the overall mixture air-fuel ratio is lean ofstoichiometry, the engine can periodically switch to operating all ofthe cylinders stoichiometric or rich. This is done to reduce the storedoxidants (e.g., NOx) in the emission control device(s). For example,this transition can be triggered based on the amount of stored NOx inthe emission control device(s), or the amount of NOx exiting theemission control device(s), or the amount of NOx in the tailpipe perdistance traveled (mile) of the vehicle.

[0114] To illustrate operation among these various modes, severalexamples of operation are described. The following are simply exemplarydescriptions of many that can be made, and are not the only modes ofoperation. As a first example, consider operation of the engine alongtrajectory A. In this case, the engine initially is operating with allcylinders in the fuel-cut mode. Then, in response to operatingconditions, it is desired to change engine operation along trajectory A.In this case, it is desired to change engine operation to operating withfour cylinders operating lean of stoichiometry, and four cylinderspumping air with substantially no injected fuel. In this case,additional fuel is added to the combusting cylinders to commencecombustion, and correspondingly increase engine torque. Likewise, it ispossible to follow the reverse trajectory in response to a decrease inengine output.

[0115] As a second example, consider the trajectory labeled B. In thisexample, the engine is operating with all cylinders combusting atsubstantially stoichiometry. In response to a decrease in desired enginetorque, 8 cylinders are operated in a fuel cut condition to provide anegative engine output torque.

[0116] As a third example, consider the trajectory labeled C. In thisexample, the engine is operating with all cylinders combusting at a leanair-fuel mixture. In response to a decrease in desired engine torque, 8cylinders are operated in a fuel cut condition to provide a negativeengine output torque. Following this, it is desired to change engineoperation to operating with four cylinders operating lean ofstoichiometry, and four cylinders pumping air with substantially noinjected fuel. Finally, the engine is again transitioned to operatingwith all cylinders combusting at a lean air-fuel mixture.

[0117] As a fourth example, consider the trajectory labeled D. In thisexample, the engine is operating with all cylinders combusting at a leanair-fuel mixture. In response to a decrease in desired engine torque, 8cylinders are operated in a fuel cut condition to provide a negativeengine output torque. Likewise, it is possible to follow the reversetrajectory in response to an increase in engine output

[0118] Continuing with FIG. 3A1, and lines 3A1-10 to 3A1-18 inparticular, an illustration of the engine output, or torque, operationfor each of the exemplary modes is described. For example, at enginespeed N1, line 3A1-10 shows the available engine output or torque outputthat is available when operating in the 8-cylinder stoichiometric mode.As another example, line 3A1-12 indicates the available engine output ortorque output available when operating in the 8-cylinder lean mode atengine speed N2. When operating in the 4-cylinder stoichiometric and4-cylinder air mode, line 3A1-14 shows the available engine output ortorque output available when operating at engine speed N3. Whenoperating in the 4-cylinder lean, 4-cylinder air mode, line 3A1-16indicates the available engine or torque output when operating at enginespeed N4. Finally, when operating in the 8-cylinder air mode, line3A1-18 indicates the available engine or torque output when operating atengine speed N5.

[0119] Referring now to FIG. 3A2, another graph is shown illustratingengine output versus engine speed. The alternative graph shows themaximum available torque that can be produced in each of 3 operatingmodes. As with regard to FIG. 3A1, note that the horizontal line doesnot necessarily correspond to zero engine brake torque. The threeoperating modes in this embodiment include:

[0120] Operating all cylinders with air pumping through andsubstantially no injected fuel (note: the throttle can be substantiallyopen, or closed, during this mode), illustrated as line 3A2-6 in theexample presented in FIG. 3A2;

[0121] Operating some cylinders at stoichiometry, and the remainingcylinders pumping air with substantially no injected fuel (note: thethrottle can be substantially open during this mode), shown as line3A2-4 in the example presented in FIG. 3A2;

[0122] Operating all cylinders substantially at stoichiometry (orslightly rich of stoichiometry) for maximum available engine torque,shown as line 3A2-2 in the example presented in FIG. 3A2.

[0123] Referring now to FIG. 3B, a routine for controlling the fuelvehicle purge is described. In general terms, the routine adjusts valve168 to control the fuel vapor purging supplied to the cylinder group 210to be combusted therein. As illustrated in FIG. 2A, the fuel vapor canbe purged to cylinders in group 210 while these cylinders are carryingout stoichiometric, rich, or lean combustion. Furthermore, the cylindersin group 212 can be carrying out combustion at stoichiometric, rich, orlean, or operating with air and substantially no injector fuel. In thisway, it is possible to purge fuel vapor while operating in the air-leanmode. Further, it is possible to purge fuel vapors while operating in astoichiometric-air mode.

[0124] Referring now specifically to FIG. 3B, in step 310, the routinedetermines whether fuel vapor purging is requested. This determinationcan be based on various parameters, such as whether the engine is in awarmed up state, whether the sensors and actuators are operating withoutdegradation, and/or whether the cylinders in group 210 are operatingunder feedback air-fuel ratio control. When the answer to step 310 isyes, the routine continues to step 312 to activate valve 168. Then, instep 314, the routine estimates the fuel vapor purge amount in the fuelvapors passing through valve 168. Note that there are various ways toestimate fuel vapor purging based on the valve position, engineoperating conditions, exhaust gas air-fuel ratio, fuel injection amountand various other parameters. One example approach is described belowherein with regard to FIG. 4. Next, in step 316, the routine adjusts theopening of valve 168 based on the estimated purge amount to provide adesired purge amount. Again, there are various approaches that can beused to produce this control action such as, for example: feedbackcontrol, feed-forward control, or combinations thereof. Also, thedesired purge amount can be based on various parameters, such as enginespeed and load, and the state of the charcoal canister in the fuel vaporpurging system. Further, the desired purge amount can be based on theamount of purge time completed.

[0125] From step 316, the routine continues to step 318 to determinewhether the estimated purge amount is less than a minimum purge value(min_prg). Another indication of whether fuel vapor purging issubstantially completed is whether the purge valve 168 has been fullyopened for a predetermined amount of operating duration. When the answerto step 318 is no, the routine continues to end. Alternatively, when theanswer to step 318 is yes, the routine continues to step 320 to disablefuel vapor purging and close valve 168. Also, when the answer to step310 is no, the routine also continues to step 322 to disable the fuelvapor purging.

[0126] In this way, it is possible to control the fuel vapor purging toa subset of the engine cylinders thereby allowing different operatingmodes between the cylinder groups.

[0127] Referring now to FIG. 3C, an example routine for controlling thesystem as shown in FIG. 2B is described. In general, the routinecontrols the fuel vapor purge valves 168 a and 168 b to selectivelycontrol fuel vapor purge in cylinder groups 210, or 212, or both. Inthis way, different sets of cylinders can be allowed to operate indifferent operating modes with fuel vapor purging, thereby providing formore equalized cylinder operation between the groups.

[0128] Referring now specifically to FIG. 3C, in step 322, the routinedetermines whether fuel vapor purging is requested as described abovewith regard to step 310 of FIG. 3B. When the answer to step 322 is yes,the routine continues to step 324 to select the cylinder group, orgroups, for purging along with selecting the purge valve or valves toactuate. The selection of cylinder groups to provide fuel vapor purgingis a function of several engine and/or vehicle operating conditions. Forexample, based on the quantity of fuel vapor purge that needs to beprocessed through the cylinders, the routine can select either onecylinder group or both cylinder groups. In other words, when greaterfuel vapor purging is required, both cylinder groups can be selected.Alternatively, when lower amounts of fuel vapor purging are required,the routine can select one of groups 210 and 212. When it is decided toselect only one of the two cylinder groups due to, for example, low fuelvapor purging requirements, the routine selects from the two groupsbased on various conditions. For example, the decision of which group toselect can be based on providing equal fuel vapor purging operation forthe two groups. Alternatively, the cylinders operating at the more leanair-fuel ratio can be selected to perform the fuel vapor purging toprovide improved combustion stability for the lean operation. Stillother selection criteria could be utilized to select the number andwhich groups to provide fuel vapor purging. Another example is that thewhen only a single cylinder group is selected, the routine alternatesbetween which group is selected to provide more even wear between thegroups. For example, the selection could attempt to provide a consistentnumber of engine cycles between the groups. Alternatively, the selectioncould attempt to provide a consistent amount of operating time betweenthe groups.

[0129] When the first group is selected, the routine continues to step326 to actuate valve 168 a. Alternatively, when the second group isselected, the routine continues to step to actuate valve 168 b in step328. Finally, when both the first and second groups are selected, theroutine continues to step 330 to actuate both valves 168 a and 168 b.

[0130] From either of steps 326, 328, or 330, the routine continues tostep 332 to estimate the fuel vapor purging amount. As described above,there are various approaches to estimate fuel vapor purge amount, suchas described below herein with regard to FIG. 4. Next, in step 334, theroutine continues to adjust the selected purge valve (or valves) basedon the estimated purge amount to provide the desired purge amount. Asdescribed above, there are various approaches to providing feedbackand/or feedforward control to provide the desired purge amount. Further,the desired purge amount can be selected based on various operatingconditions, such as, for example: engine speed and engine load.

[0131] Continuing with FIG. 3C, in step 336, the routine determineswhether the estimated purge amount is less than the minimum purge amount(min_prg). As discussed above herein with regard to step 318 of FIG. 3B.As discussed above, when the answer to step 336 is yes, the routineends. Alternatively, when the answer to step 336 is no, the routine alsocontinues to step 338 to disable fuel vapor purging. When the answer tostep 336 is no, the routine continues to the end.

[0132] In this way, it is possible to provide both cylinder groups withthe ability to operate in the air/lean, or air/stoichiometric mode andcombust fuel vapors, or the other group operates with air andsubstantially no injected fuel.

[0133] Note also that the routines of FIGS. 3A and 3B could be modifiedto operate with the configurations of FIGS. 2C-2T.

[0134] Referring now to FIG. 4, a routine for estimating fuel vaporpurge amounts is described. Note that this example shows calculationsfor use on a V8 type engine with four cylinders per bank and with twocylinders purging and two cylinders without purge on a bank asillustrated in FIG. 2A, for example. However, the general approach canbe expanded to other system configurations as is illustrated in detailbelow. The following equations describe this example configuration.

[0135] The measured air-fuel ratio in the exhaust manifold (λ_(meas))can be represented as:

λ_(meas)=(0.5dm _(aprg) /dt+0.5dm _(air) /dt)/(0.5dm _(fprg) /dt+dm_(finj1) /dt+dm _(finj2) /dt+dm _(finj3) /dt+dm _(finj4) /dt)

[0136] where:

[0137] dm_(aprg)/dt=is the mass air flow rate in the total fuel vaporpurge flow;

[0138] dm_(air)/dt=is the mass air flow rate measured by the mass airflow sensor flowing through the throttle body;

[0139] dm_(fprg)/dt=is the fuel flow rate in the total fuel vapor purgeflow;

[0140] dm_(finj1)/dt=is the fuel injection in the first cylinder of thebank coupled to the air-fuel sensor measuring λ_(meas);

[0141] dm_(finj2)/dt=is the fuel injection in the second cylinder of thebank coupled to the air-fuel sensor measuring λ_(meas);

[0142] dm_(finj3)/dt=is the fuel injection in the third cylinder of thebank coupled to the air-fuel sensor measuring λ_(meas);

[0143] dm_(finj4)/dt=is the fuel injection in the fourth cylinder of thebank coupled to the air-fuel sensor measuring λ_(meas);

[0144] When operating in with two cylinders inducting air withsubstantially no injected fuel, and fuel vapors delivered only to twocylinders carrying out combustion in that bank, this reduces to:

λ_(meas)=(0.5dm _(aprg) /dt+0.5dm _(air) /dt)/(0.5dm _(fprg) /dt+dm_(finj2) /dt+dm _(finj3) /dt)

[0145] Then, using an estimate of dm_(aprg)/dt based on manifoldpressure and purge valve position, the commanded values fordm_(finj2)/dt and dm_(finj3)/dt, the measured air-fuel ratio from thesensor for λ_(meas), and the measure airflow from the mass air flowsensor for dm_(air)/dt, an estimate of dm_(fprg)/dt can be obtained. Assuch, the concentration of fuel vapors in the purge flow can then befound as the ratio of dm_(fprg)/dt to dm_(aprg)/dt. Also, as discussedin more detail below, the fuel injection is adjusted to varydm_(finj2)/dt and dm_(finj3)/dt to provide a desired air-fuel ratio ofthe exhaust gas mixture as measured by λ_(meas). Finally, in the casewhere cylinders 1 and 4 are combusting injected fuel, the commandedinjection amounts can be used to determine the amount of fuel injectedso that the first equation can be used to estimate fuel vapors.

[0146] In this way, it is possible to estimate the fuel vapor purgecontent from a sensor seeing combustion from cylinders with and withoutfuel vapor purging.

[0147] Referring now specifically to FIG. 4, first in step 410, theroutine calculates a fresh air amount to the cylinders coupled to themeasurement sensor from the mass air flow sensor and fuel vapor purgingvalve opening degree. Next, in step 412, the routine calculates the fuelflow from the fuel injectors. Then, in step 414, the routine calculatesconcentration of fuel vapors from the air and fuel flows.

[0148] Note that if there are two fuel vapor purge valves, eachproviding vapors to separate cylinder banks and sensor sets, then theabove calculations can be repeated and the two averaged to provide anaverage amount of vapor concentration from the fuel vapor purgingsystem.

[0149] Referring now to FIG. 5, a routine is described for controlling amixture air-fuel ratio in an engine exhaust during fuel vapor purging.Specifically, the example routine of FIG. 5 can be used when a sensormeasures exhaust gases that are mixed from cylinders with and withoutfuel vapor purging.

[0150] First, in step 510, the routine determines a desired air-fuelratio (λ_(des)) for the cylinders. Then, in step 512, the routinecalculates an open loop fuel injection amount based on the estimatedpurge flow and estimated purge concentration to provide an air-fuelmixture in the cylinders with fuel vapor purging at the desired value.Then, in step 514, the routine adjusts fuel injection to the cylindersreceiving fuel vapor purging to provide the desired mixture air-fuelratio that is measured by the exhaust air-fuel ratio sensor. In thisway, the adjustment of the fuel injection based on the sensor feedbackcan not only be used to maintain the mixture air-fuel ratio at a desiredvalue, but also as an estimate of fuel vapor purging in the cylindersreceiving fuel vapors. Further, the cylinders without fuel vapors can beoperated either with air and substantially no injected fuel, or at adesired air-fuel ratio independent of the fuel vapors provided to theother cylinders.

[0151] As described above herein, there are various operating modes thatthe cylinders of engine 10 can experience. In one example, the enginecan be operated with some cylinders combusting stoichiometric or leangases, with others operating to pump air and substantially no injectedfuel. Another operating mode is for all cylinders to be combustingstoichiometric or lean gases. As such, the engine can transition betweenthese operating modes based on the current and other engine operatingconditions. As described below, under some conditions when transitioningfrom less than all the cylinders combusting to all the cylinderscombusting, various procedures can be used to provide a smoothtransition with improved engine operation and using as little fuel aspossible.

[0152] As illustrated in the graphs of FIGS. 6A-D, one specific approachto transition from four cylinder operation to eight cylinder operationis illustrated. Note that the particular example of four cylinder toeight cylinder operation could be adjusted based on the number ofcylinders in the engine such as, for example: from three cylinders tosix cylinders, from five cylinders to ten cylinders, etc. Specifically,FIG. 6A shows total engine air flow, FIG. 6B shows the fuel charge percylinder, FIG. 6C shows ignition (spark) angle, and FIG. 6D shows theair-fuel ratio of combusting cylinders.

[0153] As shown in FIGS. 6A-D, before time T1, four cylinders areinitially combusting a lean air-fuel ratio and providing a desiredengine output torque. Then, as engine airflow is decreased, the air-fuelratio approaches the stoichiometric value and the engine is operatingwith four cylinders combusting a stoichiometric air-fuel ratio andpumping air with substantially no injected fuel. Then, at time T1, theengine transitions to eight cylinders combusting. At this time, thedesire is to operate all engine cylinders as lean as possible tominimize the torque increase by doubling the number of combustingcylinders. However, since the engine typically has a lean combustionair-fuel ratio limit (as indicated by the dashed dot line in FIG. 6D),it is not possible to compensate all the increased torque by combustinga lean air-fuel ratio in all the cylinders. As such, not only is thefuel charge per cylinder decreased, but the ignition angle is alsodecreased until the airflow can be reduced to the point at which all thecylinders can be operated at the lean limit.

[0154] In other words, from time T1 to T2, engine torque is maintainedby decreasing engine airflow and retarding ignition timing until theengine can be operated with all the cylinders at the air-fuel ratiolimit to provide the same engine output as was provided before thetransition from four cylinders to eight cylinders. In this way, it ispossible to provide a smooth transition, while improving fuel economy byusing lean combustion in the enabled cylinders, as well as thepreviously stoichiometric combusting cylinders and thus reducing theamount of ignition timing retard after the transition that is required.

[0155] This improved operation can be compared to the case where thetransition is from four cylinders to eight cylinders, with the eightcylinders combusting at stoichiometry. In this case, which isillustrated by the dashed lines in FIGS. 6A-6D, a greater amount ofignition timing retard for a longer duration, is required to maintainengine torque substantially constant during the transition. As such,since this requires more ignition timing retard, over a longer duration,more fuel is wasted to produce engine output than with the approach ofthe solid lines in FIGS. 6A-6D, one example of which is described in theroutine of FIG. 7.

[0156] Referring now to FIG. 7, a routine is described for controlling atransition from less than all the cylinders combusting to all thecylinders combusting, such as the example from four cylinders to eightcylinders illustrated in FIGS. 6A-D.

[0157] First, in step 710, the routine determines whether a transitionhas been requested to enable the cylinders operating to pump air andsubstantially no injected fuel. When the answer to step 710 is yes, theroutine continues to step 712 to determine whether the system iscurrently operating in the air-lean mode. When the answer to step 712 isyes, the routine transitions the engine to the air-stoichiometric modeby decreasing engine airflow. Next, from step 714, or when the answer tostep 712 is no, the routine continues to step 716. In step 716, theroutine calculates a lean air-fuel ratio with all cylinders operating(λ_(f)) at the present airflow to provide the current engine torque. Inthe example of transitioning from four cylinders to eight cylinders,this air-fuel ratio is approximately 0.5 if the current operatingconditions are in the air-stoichiometric mode. In other words, all thecylinders would require half the fuel to produce the same torque as halfthe cylinders at the current amount of fuel.

[0158] Next, in step 718, the routine calculates the lean limit air-fuelratio (λ_(LL)) for the conditions after the transition. In other words,the routine determines the combustion stability lean limit which isavailable after the transition for the operating conditions present.Then, in step 720, the routine determines whether the calculated leanair-fuel ratio to maintain engine torque (λ_(f)) is greater than thelean limit air-fuel ratio. If the answer to step 720 is no, thetransition is enabled without ignition timing retard. In this case, theroutine transitions the cylinders to the new air-fuel ration calculatedin step 716 to maintain engine torque.

[0159] However, the more common condition is that the required air-fuelratio to maintain engine torque is greater than the lean limit for theoperating conditions. In this case, the routine continues to step 722 totransition the air-fuel ratio at the lean air-fuel limit and compensatethe torque difference via the ignition timing retard. Further, theairflow is reduced until the engine can operate at the lean air-fuelratio limit (or within a margin of the limit) without ignition timingretard.

[0160] In this way, the transition to enabling cylinders with leancombustion can be utilized to improve fuel economy and maintain enginetorque during the transition. Thus, not only is the torque balanced overthe long term, but also over the short term using air-fuel enleanment inaddition to ignition timing retard, if necessary. Further, thistransition method achieves the a synergistic effect of rapid catalystheating since the ignition timing retard and enleanment help increaseheat to the exhaust system to rapidly heat any emission control devicescoupled to deactivated cylinders. Note that various modifications can bemade to this transition routine. For example, if transitioning to enablepurging of NOx stored in the exhaust system, rich operation can followthe enleanment once airflow has been reduced.

[0161] Referring now to FIG. 8, a routine is described for controllingengine cylinder valve operation (intake and/or exhaust valve timingand/or lift, including variable cam timing, for example) depending onengine conditions and engine operating modes. In general terms, theroutine of FIG. 8 allows engine cylinder valve operation for differentgroups of cylinders during engine starting to help compensate forvariations in ignition timing between the groups.

[0162] First, in step 810, the routine determines whether the presentconditions represent an engine starting condition. This can bedetermined by monitoring if the engine is being turned by a startingmotor. Note however, that engine starting can include not only theinitial cranking by the starter, but also part of the initial warm upphase from a cold engine condition. This can be based on variousparameters, such as engine speed, time since engine start, or others.Thus, when the answer to step 810 is yes, the routine then determineswhether the engine is already in a warmed up condition in step 812. Thiscan be based on, for example, engine coolant temperature.

[0163] When the answer to step 812 is no, the routine sets the flag(flag_LS) to one. Otherwise, the flag is set to zero at 816. Next, theroutine continues to step 818 where a determination is made as towhether split ignition operation is requested. One example of splitignition operation includes the following method for rapid heating ofthe emission control device when an emission control device(s) is belowa desired operating temperature. Specifically, in this approach, theignition timing between two cylinders (or two or more cylinder groups)is set differently. In one example, the ignition timing for the firstgroup (spk_grp_(—)1) is set equal to a maximum torque, or best, timing(MBT_spk), or to an amount of ignition retard that still provides goodcombustion for powering and controlling the engine. Further, theignition timing for the second group (spk_grp_(—)2) is set equal to asignificantly retarded value, for example −29°. Note that various othervalues can be used in place of the 29° value depending on engineconfiguration, engine operating conditions, and various other factors.Also, the power heat flag (ph_enable) is set to zero.

[0164] The amount of ignition timing retard for the second group(spk_grp_(—)2) used can vary based on engine operating parameters, suchas air-fuel ratio, engine load, and engine coolant temperature, orcatalyst temperature (i.e., as catalyst temperature rises, less retardin the first and/or second groups, may be desired). Further, thestability limit value can also be a function of these parameters.

[0165] Also note, as described above, that the first cylinder groupignition timing does not necessarily have to be set to maximum torqueignition timing. Rather, it can be set to a less retarded value than thesecond cylinder group, if such conditions provide acceptable enginetorque control and acceptable vibration. That is, it can be set to thecombustion stability spark limit (e.g., −10 degrees). In this way, thecylinders on the first group operate at a higher load than theyotherwise would if all of the cylinders were producing equal engineoutput. In other words, to maintain a certain engine output (forexample, engine speed, engine torque, etc.) with some cylindersproducing more engine output than others, the cylinders operating at thehigher engine output produce more engine output than they otherwisewould if all cylinders were producing substantially equal engine output.

[0166] An advantage to the above aspect is that more heat can be createdby operating some of the cylinders at a higher engine load withsignificantly more ignition timing retard than if operating all of thecylinders at substantially the same ignition timing retard. Further, byselecting the cylinder groups that operate at the higher load, and thelower load, it is possible to minimize engine vibration. Thus, the aboveroutine starts the engine by firing cylinders from both cylinder groups.Then, the ignition timing of the cylinder groups is adjusted differentlyto provide rapid heating, while at the same time providing goodcombustion and control.

[0167] Also note that the above operation provides heat to both thefirst and second cylinder groups since the cylinder group operating at ahigher load has more heat flux to the catalyst, while the cylinder groupoperating with more retard operates at a high temperature.

[0168] Note that in such operation, the cylinders have a substantiallystoichiometric mixture of air and fuel. However, a slightly lean mixturefor all cylinders, or part of the cylinders, can be used.

[0169] Also note that all of the cylinders in the first cylinder groupdo not necessarily operate at exactly the same ignition timing. Rather,there can be small variations (for example, several degrees) to accountfor cylinder to cylinder variability. This is also true for all of thecylinders in the second cylinder group. Further, in general, there canbe more than two cylinder groups, and the cylinder groups can have onlyone cylinder.

[0170] Further note that, as described above, during operation accordingto one example embodiment, the engine cylinder air-fuel ratios can beset at different levels. In one particular example, all the cylinderscan be operated substantially at stoichiometry. In another example, allthe cylinders can be operated slightly lean of stoichiometry. In stillanother example, the cylinders with more ignition timing retard areoperated slightly lean of stoichiometry, and the cylinders with lessignition timing retard are operated slightly rich of stoichiometry.Further, in this example, the overall mixture of air-fuel ratio is setto be slightly lean of stoichiometry. In other words, the lean cylinderswith the greater ignition timing retard are set lean enough such thatthere is more excess oxygen than excess rich gasses of the rich cylindergroups operating with less ignition timing retard.

[0171] Continuing with FIG. 8, when the answer to step 818 is yes, theroutine enables the split ignition operations in step 820 by setting theflag (PH_ENABLE_Flg) to one.

[0172] Then, in step 822, the desired valve operation (in this casevalve timing) for the first and second group of cylinders is calculatedseparately and respectively based on the conditions of the cylindergroups, including the air flow, air/fuel ratio, engine speed, enginetorque (requested and actual), and ignition timing. In this way, anappropriate amount of air charge and residual charge can be provided tothe different cylinder groups to better optimize the conditions for therespective ignition timing values used in the cylinders.

[0173] The desired variable cam timings for the cylinder groups can alsobe based on various other parameters, such as catalyst temperature(s)and/or whether flag_CS is set to zero or one. When operating in thesplit ignition operation, at least during some conditions, this resultsin different VCT settings between different cylinder groups to provideimproved engine operation and catalyst heating. In this way, the airflow to the cylinder with more advanced ignition timing can be used tocontrol engine output torque, as well as the torque imbalance betweenthe cylinder groups. Further, the airflow to the cylinder with moreretarded ignition timing can be used to control the combustionstability, or heat flux produced. Also, if the engine is not equippedwith VCT, but rather variable valve lift, or electrically actuatedvalves, then different airflow can be provided to different cylindersvia valve lift, or variation of timing and/or lift of the electricallyactuated valves. Furthermore, if the engine is equipped with multiplethrottle valves (e.g., one per bank), then airflow to each group can beadjusted via the throttle valve, rather than via variations in VCT.

[0174] Continuing with FIG. 8, when the answer to step 818 is no, theroutine continues to step 824 where a determination is made as towhether fuel injector cut-out operation of a cylinder, or cylindergroups, is enabled. When the answer to step 824 is yes, the routinecontinues to step 826 to calculate the desired cam timing (s) foroperating cylinder group(s) taking into account the cylinder cut-outoperation. In other words, different valve timings can be selected, atleast during some conditions, based on whether cylinder cut-outoperation is engaged. Thus, the VCT timing for the respective cylindergroups is based on the air-fuel ratio of combustion in the groupcombusting air and injected fuel, while the VCT timing for the groupwithout fuel injection is selected to, in one example, minimize enginepumping losses. Alternatively, when transitioning into, or out of, thepartial or total cylinder cut-out operation, the VCT timing for therespective cylinder groups is adjusted based on this transition. Forexample, when enabling combustion of cylinder previous in cylindercut-out operation, the VCT timing is adjusted to enable efficient andlow emission re-starting of combustion, which can be a different optimaltiming for the cylinders which were already carrying out combustion ofair and injected fuel. This is described in more detail below withregard to FIG. 12, for example.

[0175] Alternatively, when the answer to step 824 is no, the valvetiming for the cylinder groups is selected based on engine speed andload, for example.

[0176] In this way, it is possible to select appropriate valve timing toimprove cylinder cut-out operation. When firing groups coincide with VCT(or bifurcated intake groups), it is possible to optimize the amount ofcatalyst heating (or efficient engine operation) depending on thevehicle tolerance to different types of excitation (NVH) given theoperating conditions.

[0177] Specifically, in one example, NVH performance can be improved byreducing the airflow to cylinders with significantly retarded ignitiontiming to reduce any effect of combustion instability that may occur.Likewise, in another example, engine torque output can be increased,without exacerbating combustion instability, by increasing airflow tothe cylinder(s) with more advanced ignition timing. This can beespecially useful during idle speed control performed via an idle bypassvalve, or via the electronic throttle, where even though total airflowis being increased, that increased airflow can be appropriatelyallocated to one cylinder group or another depending on the ignitiontiming split used.

[0178] Note that an alternative starting routine is described in FIG.34.

[0179] Referring now to FIG. 9, a routine is described for identifyingpedal tip-out conditions, and using such information to enable ordisable fuel injection to cylinders, or cylinder groups, of the engine.First, in step 910, the routine identifies whether a tip-out conditionhas been detected. Note that there are various approaches to detecting atip-out condition, such as, for example: detecting if whether the pedalhas been released by the vehicle driver's foot, whether a requestedengine output has decreased below a threshold value (for example, belowzero value engine brake torque), whether a requested wheel torque hasdecreased below a threshold level, or various others. When the answer tostep 910 is yes and a tip-out condition has been detected, the routinecontinues to step 912. In step 912, the routine determines whether therequested engine output is less than threshold T1. In one example, thisthreshold is the minimum negative engine output that can be achievedwith all the cylinders combusting. This limit can be set due to variousengine combustion phenomena, such as engine misfires, or significantlyincreased emissions. Also note that various types of requested engineoutput can be used, such as, for example: engine torque, engine braketorque, wheel torque, transmission output torque, or various others.When the answer to step 912 is yes, the routine continues to step 914.In step 914, the routine enables a fuel cut operation, which isdiscussed in more detail below with regard to FIG. 10. Alternatively,when the answer to either step 910 or 912 is no, the routine continuesto step 916 in which combustion in all the cylinders of the engine iscontinued.

[0180] Note that the fuel cut operation enabled in step 914 can bevarious types of cylinder fuel cut operation. For example, only aportion of the engine's cylinders can be operated in the fuel cutoperation, or a group of cylinders can be operated in the fuel cutoperation, or all of the engine cylinders can be operated in the fuelcut operation. Furthermore, the threshold T1 discussed above with regardto step 912 can be a variable value that is adjusted based on thecurrent engine conditions, including engine load and temperature.

[0181] Referring now to FIG. 10, an example routine is described forcontrolling fuel cut operation, which can be used with a variety ofsystem configurations, such as, for example, FIGS. 2A-2H. First, in step1010, the routine determines whether fuel cut operation has been enabledas discussed above with regard to step 914 of FIG. 9. When the answer tostep 1010 is yes, the routine continues to step 1012. In step 1012, theroutine determines the number of cylinder groups to disable based on therequested engine output and current engine and vehicle operatingconditions. These operating conditions include the catalyst operatingconditions, temperature (engine temperature and/or catalyst temperature)and engine speed. Next, in step 1014, the routine determines the numberof cylinders in the groups to be disabled based on the requested engineoutput and engine and vehicle operating conditions. In other words, theroutine first determines the number of cylinder groups to be disabled,and then determines within those groups, the number of cylinders of thegroups to be disabled. These determinations are also selected dependingon the engine and exhaust catalyst configuration. For example, in casesusing a downstream lean NOx trap, in addition to disabling cylinders,the remaining active cylinders can be operated at a lean air-fuel ratio.

[0182] Continuing with FIG. 10, in step 1016, the routine determineswhether the requested engine output is greater than a threshold T2, suchas when a vehicle driver tips-in to the vehicle pedal. When the answerto step 1016 is no, the routine continues to step 1018 to determinewhether temperature of the emission control devices coupled to disabledcylinders is less than a minimum temperature (min_temp). As such, theroutine monitors the requested engine output and the temperature of theemission control devices to determine whether to re-enable cylindercombustion in the activated cylinders. Thus, when the answer to eitherstep 1016 or 1018 is yes, the routine continues to step 1020 to disablefuel cut operation and enable combustion. This enabling can enable allthe cylinders to return to combustion or only a part of the activatedcylinders to return to combustion. Whether all or only a portion of thecylinders are reactivated depends on various engine operating conditionsand on the exhaust catalyst configuration. For example, when three-waycatalysts are used without a lean NOx trap, all of the cylinders may beenabled to carry out combustion. Alternatively, when a downstream leanNOx trap is used, all or only a portion of the cylinders may bere-enabled at a lean air-fuel ratio, or some of the cylinders can bere-enabled to carry out stoichiometric combustion.

[0183] Note that before the fuel cut operation is enabled, the enginecan be operating with all the cylinders carrying out lean,stoichiometric, or rich engine operation.

[0184] Referring now to FIG. 11, a routine is described for performingidle speed control of the engine, taking into account fuel vaporpurging. First, in step 1110, the routine determines whether idle speedcontrol conditions are present. Idle speed conditions can be detected bymonitoring whether the pedal position is lower than a preselectedthreshold (indicating the driver's foot is off the pedal) and the enginespeed is below a threshold speed (for example 1000 RPM). When the answerto step 1110 is yes, the routine continues to step 1112. In step 1112,the routine determines whether lean combustion is enabled based on thecurrent engine operating conditions, such as exhaust temperature, enginecoolant temperature, and other conditions, such as whether the vehicleis equipped with a NOx trap. When the answer to step 1112 is no, theroutine continues to step 1114.

[0185] In step 1114, the routine maintains the desired idle speed viathe adjustment of air flow to the engine. In this way, the air flow isadjusted so that the actual speed of the engine approaches the desiredidle speed. Note that the desired idle speed can vary depending onoperating conditions such as engine temperature. Next, in step 1116, theroutine determines whether fuel vapors are present in the engine system.In one example, the routine determines whether the purge valve isactuated. When the answer to step 1116 is yes, the routine continues tostep 1118. In step 1118, the routine adjusts the fuel injection amount(to the cylinders receiving fuel vapors) to maintain the desiredair-fuel ratio, as well as compensate for the fuel vapors, while fuelinjected to cylinders combusting without fuel vapors (if any) can be setto only a feed-forward estimate, or further adjusted based on feedbackfrom the exhaust gas oxygen sensor. Thus, both cylinders with andwithout fuel vapor are operated at a desired air-fuel ratio by injectingless fuel to the cylinders with fuel vapors. In one example, the desiredcombustion air-fuel ratio oscillates about the stoichiometric air-fuelratio, with feedback from exhaust gas oxygen sensors from the engine'sexhaust. In this way, the fuel injection amount in the cylinders withfuel vapors is compensated, while the fuel injection amount to cylindersoperating without fuel vapors is not affected by this adjustment, andall of the cylinders combusting are operated about stoichiometry.

[0186] Next, in step 1120, the routine determines whether the fuelinjection pulse width (to the cylinders with fuel vapors) is less than aminimum value (min_pw). When the answer to step 1120 is yes, the routinecontinues to step 1122 to disable fuel vapor purging and close the purgevalve (s). In this way, the routine prevents the fuel injection pulsewidth from becoming lower than a minimum allowed pulse width to operatethe injectors.

[0187] When the answer to either step 1116, or 1120 is no, the routinecontinues to the end.

[0188] When the answer to step 1112 is yes, the routine continues tostep 1124. Then, in step 1124, the routine maintains the desired idlespeed via adjustment of fuel injection. In this way, the fuel injectionamount is adjusted, so that the actual speed of the engine approachesthe desired idle speed. Note that this lean combustion conditionsincludes conditions where some cylinders operate with a lean air-fuelratio, and other cylinders operate without injected fuel. Next, in step1126, the routine determines whether fuel vapors are present in theengine (similar to that in step 1116). When the answer is yes, theroutine continues to step 1128 where air flow is adjusted to maintainthe air-fuel ratio in the combusting cylinders and compensate for thefuel vapors. Note that there are various ways to adjust the air flow tothe cylinders carrying out combustion, such as by adjusting the throttleposition of the electronically controlled throttle plate. Alternatively,air flow can be adjusted by changing valve timing and/or lift, such asby adjusting a variable cam timing actuator.

[0189] Next, in step 1130, a routine determines whether the cylinderair-fuel ratio (of cylinders carrying out combustion) is less than aminimum value (afr_min). In one example, this is a minimum lean air-fuelratio, such as 18:1. In addition, the routine monitors whether air flowis at the maximum available air flow for the current engine operatingconditions. If not, the engine first attempts to increase air flow byfurther opening the throttle, or adjusting valve timing and/or lift.However, when air flow is already at a maximum available amount, theroutine continues to step 1132 to disable lean combustion. The routinemay still allow continued cylinder fuel cut-out operation since thisoperation provides for maximum fuel vapor purging in a stoichiometriccondition as will be discussed below.

[0190] When the answer to either step 1110, 1126, or 1130, is no, theroutine continues to the end.

[0191] In this way, it is possible to operate with fuel vapor purgingand improve operation of both lean and stoichiometric combustion.Specifically, by using fuel injection to maintain idle speed during leanconditions, and air flow to maintain idle speed during non-leanconditions, it is possible to provide accurate engine idle speed controlduring both conditions. Also, by disabling lean operation, yetcontinuing to allow cylinder fuel cut-out operation, when the fuelvapors are too great to allow lean combustion, it is possible to improvethe quantity of fuel vapor purge that can be processed. In other words,during cylinder fuel cut-out operation, all the fuel vapors are fed to aportion of the cylinders, for example as shown in FIG. 2C. However,since less than all the cylinders are carrying out the combustion togenerate engine output, these cylinders operate at a higher load, andtherefore a higher total requirement of fuel to be burned. As such, theengine is less likely to experience conditions where the fuel injectorsare less than the minimum pulse width than compared if all the cylinderswere carrying out combustion with fuel vapors. In this way, improvedfuel vapor purging capacity can be achieved.

[0192] Referring now to FIGS. 12A and 12B, routines are described forcontrolling cylinder valve adjustment depending, in part, on whethersome or all of the cylinders are operating an a fuel-cut state. Ingeneral, the routine adjusts the cylinder valve timing, and/or valvelift, based on this information to provide improved operation. Also, theroutine of FIG. 12A is an example routine that can be used for systemconfigurations such as those shown in FIGS. 2N, 20, 2P, 2S and/or 2T.The routine of FIG. 12B is an example routine that can be used forsystem configurations such as those shown in FIGS. 2I and 2J.

[0193] First, in step 1210, the routine determines whether the engine isoperating in a full or partial fuel injector cut-out operation. When theanswer to step 1210 is yes, the routine continues to step 1212. In step1212, the routine determines a desired cylinder valve actuation amountfor a first and second actuator. In this particular example, where afirst and second variable cam timing actuator are used to adjust camtiming of cylinder intake and/or exhaust valves, the routine calculatesa desired cam timing for the first and second actuator (VCT_DES1 andVCT_DES2). These desired cam timing values are determined based on thecylinder cut-out condition, as well as engine operating conditions suchas the respective air-fuel ratios and ignition timing values betweendifferent cylinder groups, throttle position, engine temperature, and/orrequested engine torque. In one embodiment, the operating conditionsdepend on operating mode. Specifically, in addition to engine speedversus torque, the following conditions are considered in an idle speedmode: engine speed, closed pedal, crank start, engine temperature, andair charge temperature. In addition to engine speed versus torque, thefollowing conditions are considered in a part throttle or wide openthrottle condition: rpm, desired brake torque, and desired percenttorque.

[0194] In one example, where the routine is applied to a system such asin FIG. 2S or 2T, the routine can further set a cam timing per bank ofthe engine, where the cylinder groups have some cylinders from each bankin the group. Thus, a common cam timing is used for both cylinders withand without combustion from injected fuel. As such, the desired camtiming must not only provide good combustion in the cylinders carryingout combustion, but also maintain a desired manifold pressure byadjusting airflow though the engine, along with the throttle. Note thatin many conditions, this results in a different cam timing for thecombusting cylinders than would be obtained if all of the cylinders werecarrying out combustion in the cylinder group.

[0195] Alternatively, when the answer to step 1210 is no, the routinecontinues to step 1214 to calculate the desired valve actuator settings(VCT_DES1 and VCT_DES2) based on engine conditions, such as enginespeed, requested engine torque, engine temperature, air-fuel ratio,and/or ignition timing.

[0196] From either of steps 1212 or 1214, the routine continues to step1216 where a determination is made as to whether the engine istransitioning into, or out of, full or partial fuel injector cut-outoperation. When the answer to step 1216 is no, the routine continues tostep 1218 where no adjustments are made to the determined desiredcylinder valve values.

[0197] Otherwise, when the answer to step 1216 is yes, the routinecontinues to step 1220 where the routine determines whether thetransition is to re-enable fuel injection, or cut fuel injectionoperation. When it is determined that a cylinder, or group of cylinders,is to be re-enabled, the routine continues to step 1222. Otherwise, theroutine continues to the end.

[0198] In step 1222, the routine adjusts the desired cam timing values(VCT_DES1 and/or VCT_DES2) of cylinder valves coupled to cylinders beingre-enabled to a re-starting position (determine based on engine coolanttemperature, airflow, requested torque, and/or duration of fuel-cutoperation). In this way, it is possible to have improved re-starting ofthe cylinders that were in fuel-cut operation. In the case where bothcylinders are operated in a fuel cut operation, all of the cylinders canbe restarted at a selected cam timing that provides for improvedstarting operation.

[0199] Note that due to different system configurations, this may alsoadjust cam timing of cylinders already carrying out combustion. As such,additional compensation via throttle position or ignition timing can beused to compensate for increases or decreases engine output due to theadjustment of cam timing before the transition. The details of thetransition are discussed in more detail above and below, such asregarding FIG. 6, for example.

[0200] Referring now to FIG. 12B, an alternative embodiment forcontrolling cylinder valve actuation based on fuel-cut operation isdescribed. First, in step 1230, the routine determines whether theengine is operating in a full or partial fuel injector cut-outoperation. When the answer to step 1230 is yes, the routine continues tostep 1232. In step 1232, the routine determines a desired cylinder valveactuation amount for an actuator coupled to a group of cylinders inwhich fuel injection is disabled. In one example, this is a desired camtiming value. Further, the routine also calculates an adjustment tothrottle position, along with the cam timing, to adjust the engineoutput to provide a requested engine output. In one example, therequested engine output is a negative (braking) engine torque value.Further, in step 1232, the routine adjusts the cam timing for thecombusting cylinders (if any) based on conditions in those combustingcylinders.

[0201] Alternatively, the routine can set the desired cylinder valveactuation amount for deactivated cylinders to provide a desired enginepumping loss amount, since adjusting the cam timing of the cylinderswill vary the intake manifold pressure (and airflow), thus affectingengine pumping losses. Note that in some cases, this results in adifferent cam timing being applied to the group of cylinders combustingthan the group of cylinders in fuel-cut operation.

[0202] Alternatively, when the answer to step 1230 is no, the routinecontinues to step 1234 to calculate the desired valve actuator settings(VCT_DES1 and VCT_DES2) based on engine conditions, such as enginespeed, requested engine torque, engine temperature, air-fuel ratio,and/or ignition timing as shown in step 1214.

[0203] From either of steps 1232 or 1234, the routine continues to step1236 where a determination is made as to whether the engine istransitioning into, or out of, full or partial fuel injector cut-outoperation. When the answer to step 1236 is no, the routine continues tostep 1238 where no adjustments are made to the determined desiredcylinder valve values.

[0204] Otherwise, when the answer to step 1236 is yes, the routinecontinues to step 1240 where the routine determines whether thetransition is to re-enable fuel injection, or cut fuel injectionoperation. When it is determined that a cylinder, or group of cylinders,is to be re-enabled, the routine continues to step 1242. Otherwise, theroutine continues to the end.

[0205] In step 1242, the routine adjusts the cam timing actuatorscoupled to disabled cylinders to a re-starting position. Note that thecylinders can re-start at a lean air-fuel ratio, a rich air-fuel ratio,or at stoichiometry (or to oscillate about stoichiometry). In this way,by moving the cam timing that provides for improved starting, whileoptionally leaving the cam timing of cylinders already combusting at itscurrent condition, it is possible provide improved starting operation.

[0206] Referring now to FIGS. 13A and 13B, routines and correspondingexample results are described for controlling partial and full cylindercut operation to reestablish the oxygen storage amount in the downstreamthree-way catalyst, as well as to reestablish the fuel puddle in theintake manifold to improve transient fuel control. Note that theroutines FIGS. 13A and 13C can be carried out with various systemconfigurations as represented in FIG. 2. For example, the routine ofFIG. 13A can be utilized with the system of FIG. 2Q, for example.Likewise, the routine of FIG. 13C can be utilized with the system ofFIG. 2R. Referring now specifically to FIG. 13A, in step 1302, theroutine determines whether partial cylinder fuel cut-out operation ispresent. When the answer to step 1302 is yes, the routine continues tostep 1304. In step 1304, the routine determines whether the cylinderscarrying out combustion are operating about stoichiometry. When theanswer to step 1304 is yes, the routine continues to step 1306. In step1306, the routine determines whether transition to operate both cylindergroups to combust an air-fuel ratio that oscillates about stoichiometryhas been requested by the engine control system. When the answer to anyof steps 1302, 1304, or 1306 are no, the routine continues to the end.

[0207] When the answer to step 1306 is yes, the routine continues tostep 1308. In step 1308, the routine enables fuel injection in thedisabled cylinder group at a selected rich air-fuel ratio, whilecontinuing operation of the other cylinder carrying out combustion aboutstoichiometry. The selected rich air-fuel ratio for the re-enabledcylinders is selected based on engine operating conditions such as, forexample: catalyst temperature, engine speed, catalyst space velocity,engine load, and such or requested engine torque. From step 1308, theroutine continues to step 1310, where a determination is made as towhether the estimated actual amount of oxygen stored in the downstreamthree-way catalyst (O2_d_act) is greater than a desired amount of oxygen(O2_d_des). When the answer to step 1310 is yes, the routine continuesto step 1312 to continue the rich operation of the re-enabled cylindergroup at a selected rich air-fuel ratio, and the oscillation aboutstoichiometry of the air-fuel ratio of the already combusting cylinders.As discussed above with regard to step 1308, the rich air-fuel ratio isselected based on engine operating conditions, and various dependingupon them. From step 1312, the routine returns to step 1310 to againmonitor the amount of oxygen stored in the downstream three-waycatalyst. Alternatively, the routine of FIG. 13A can also monitor aquantity of fuel in the puddle in the intake manifold of the cylindersthat are being re-enabled in step 1310.

[0208] When the answer to step 1310 is no, the routine continues to step1314 which indicates that the downstream three-way catalyst has beenreestablished at a desired amount of stored oxygen between the maximumand minimum amounts of oxygen storage, and/or that the fuel puddle inthe intake manifold of the various enabled cylinders has beenreestablished. As such, in step 1314, the routine operates both groupsabout stoichiometry. In this way, it is possible to re-enable thecylinders from a partial cylinder cut-out operation and reestablish theemission control system to a situation in which improved emissioncontrol can be achieved.

[0209] The operation of FIG. 13A is now illustrated via an example asshown in FIGS. 13B1 and 13B2. FIG. 13B1 shows the air-fuel ratio ofgroup 1, while FIG. 13B2 shows the air-fuel ratio of group 2. At timeT0, both cylinder groups operate to carry out combustion about thestoichiometric value. Then, at time T1, it is requested to transitionthe engine to partial cylinder cut operation, and therefore the cylindergroup 1 is operating at a fuel cut condition. As shown in FIG. 13B1, theair-fuel ratio is infinitely lean and designated via the dashed linethat is at a substantially lean air-fuel ratio. Then, at time T2, it isdesired to re-enable the partially disabled cylinder operation, andtherefore the cylinder group 1 is operated at a rich air-fuel ratio asshown in FIG. 13B1, this rich air-fuel ratio varies as engine operatingconditions change. The rich operation of group 1 and the stoichiometricoperation of group 2 continues until time T3, at which point it isdetermined that the downstream emission control device has beenreestablished to an appropriate amount of oxygen storage. As describedelsewhere herein, the identification of when to discontinue the richregeneration operation can be based on estimates of stored oxygen,and/or based on when a sensor downstream of the downstream emissioncontrol device switches. At time T3, both cylinder groups are returnedto stoichiometric operation, as shown in FIGS. 13B1 and 13B2.

[0210] As such, improved engine operation is achieved since the secondcylinder group can remain combusting at stoichiometry throughout thesetransitions, yet the downstream emission control device can have itsoxygen storage reestablished via the rich operation of the firstcylinder group. This reduces the amount of transitions in the secondcylinder group, thereby further improving exhaust emission control.

[0211] Referring now to FIG. 13C, a routine is described for controllingcylinder cut-out operation where both cylinder groups are disabled.First, in step 1320, the routine determines whether all cylinders arepresently in the cylinder cut operation. When the answer to step 1320 isyes, the routine continues to step 1322 to determine whether thecylinders will be carrying out stoichiometric combustion when enabled.When the answer to step 1322 is yes, the routine continues to step 1324to determine whether the transition of one or two groups is requested tobe enabled. In other words, the routine determines whether it has beenrequested to enable only one cylinder group, or to enable two cylindergroups to return to combustion. When the answer to step 1324, or step1322, or step 1320, is no, the routine ends.

[0212] Alternatively, when in step 1324, it is requested to enable bothcylinder groups, the routine continues to step 1326. In step 1326, theroutine operates fuel injection in both cylinder groups at a selectedrich air-fuel ratio. Note that the groups can be operated at the samerich air-fuel ratio, or different rich air-fuel ratios. Likewise, theindividual cylinders in the groups can be operated at different richair-fuel ratios. Still further, in an alternative embodiment, only someof the cylinders are operated rich, with the remaining cylindersoperating about stoichiometry.

[0213] From step 1326, the routine continues to step 1328. In step 1328,the routine determines whether the estimated amount of oxygen stored inthe upstream three-way catalyst coupled to the first group (O2_u1_act)is greater than a desired amount of stored oxygen for that catalyst(O2_u1_des). When the answer to step 1320 is no, indicating that theoxygen storage amount has not yet been reestablished in that device, theroutine continues to step 1330 to calculate whether the estimated actualamount of oxygen stored in the emission upstream three-way catalystcoupled to the second group (O2_u2_act) is greater than its desiredamount of stored oxygen (O2_u2_des). When the answer to step 1330 is no,indicating that neither upstream three-way catalyst coupled to therespective first and second groups' cylinders has been reestablished totheir respective desired amounts of stored oxygen, the routine continuesto step 1326, where rich operation in both cylinder groups is continuedat the selected air-fuel ratio. Also note that the selected richair-fuel ratio is adjusted based on engine operating conditions asdescribed above herein with regard to step 1308, for example.

[0214] When the answer to step 1328 is yes, indicating that the upstreamthree-way catalyst coupled to the first cylinder group has had itsoxygen amount reestablished, the routine continues to step 1332 totransition the first group to operate about stoichiometry. Next, theroutine continues to step 1334 where it continues operation of thesecond a t the selected rich air-fuel ratio and the second group tocombust an air-fuel mixture that oscillates about stoichiometry. Then,the routine continues to step 1336, where a determination is made as towhether the estimated amount of stored oxygen in a downstream three-waycatalyst (which is coupled to at least one of the upstream three-waycatalysts, if not both) is greater than its desired amount of storedoxygen. When the answer to step 1336 is no, the routine returns to step1334 to continue the rich operation in the second group, and thestoichiometric operation in the first group. Alternatively, when theanswer to step 1336 is yes, the routine continues to step 1338 totransition both cylinder groups to operate about stoichiometry.

[0215] Continuing with FIG. 13C, when the answer to step 1330 is yes,indicating that the oxygen amount has been reestablished in the emissionupstream three-way catalyst coupled to the second group, the routinetransitions the second group to stoichiometry in step 1342. Then, instep 1344, the routine continues to operate the first cylinder group atthe rich air-fuel ratio and the second cylinder group aboutstoichiometry. Then, the routine continues to step 1346 to again monitorthe oxygen storage amount in the downstream three-way catalyst. Fromstep 1346, when the downstream fuel catalyst has not yet had enoughoxygen depleted to reestablish the oxygen amount, the routine returns tostep 1344. Alternatively, when the answer to step 1346 is yes, theroutine also transitions to step 1338 to have both cylinder groupsoperating about stoichiometry.

[0216] From step 1324, when it is desired to transition only onecylinder group to return to combustion, the routine continues to step1350 to enable fuel injection in one cylinder group at the selected richair-fuel ratio and continue fuel cut operation in the other cylindergroup. This operation is continued in step 1352. Note that for thisillustration, it is assumed that in this case the first cylinder grouphas been enabled to carry out combustion, while the second cylindergroup has continued operating at fuel cut operation. However, whichcylinder group is selected to be enabled can vary depending on engineoperating conditions, and can be alternated to provide more evencylinder ware.

[0217] From step 1352, the routine continues to step 1354, where adetermination is made as to whether the estimated actual amount ofstored oxygen in the upstream three-way catalyst coupled to the firstcylinder group (O2_u1_act) is greater than the desired amount(O2_u1_des). When the answer to step 1354 is no, the routine returns tostep 1352. Alternatively, when the answer to step 1354 is yes, theroutine continues to step 1356 to operate a first cylinder group aboutstoichiometry and continue the operation of the second cylinder group inthe fuel cut operation. Finally, in step 1358, the routine transfers toFIG. 13A to monitor further requests to enable the second cylindergroup.

[0218] In this way, it is possible to allow for improved re-enablementof cylinder fuel cut operation to properly establish the oxygen storagenot only in the upstream three-way catalyst, but also in the downstreamthree-way catalyst without operating more cylinders rich than isnecessary. As described above, this can be accomplished using anestimate of stored oxygen in an exhaust emission control device.However, alternatively, or in addition, it is also possible to useinformation from a centrally mounted air-fuel ratio sensor. For example,a sensor that is mounted at a location along the length of the emissioncontrol device, such as before the last brick in the canister, can beused. In still another approach, downstream sensor(s) can be used todetermine when regeneration of the oxygen storage is sufficientlycompleted.

[0219] Example operation of FIG. 13C is illustrated in the graphs ofFIGS. 13D1 and 13D2. Like FIGS. 13B1 and B2, FIG. 13D1 shows theair-fuel ratio of the first cylinder group and FIG. 13D2 shows theair-fuel ratio of the second cylinder group. At time T0, both cylindergroups are operating to carry out combustion about the stoichiometricair-fuel ratio. Then, at time T1, it is requested to disable fuelinjection in both cylinder groups. As such, both cylinder groups areshown to operate at a substantially infinite lean air-fuel ratio untiltime T2. At time T2, it is requested to enable combustion in bothcylinder groups. As such, both cylinder groups are shown operating at arich air-fuel ratio. As illustrated in the figures, the level richnessof this air-fuel ratio can vary depending on operating conditions. Fromtimes T2 to T3, the oxygen saturated upstream first and second three-waycatalysts are having the excess oxygen reduced to establish a desiredamount of stored oxygen in both the catalysts. At time T3, the upstreamthree-way catalyst coupled to the second group has reached the desiredamount of stored oxygen and therefore the second cylinder istransitioned to operate about stoichiometry. However, since thedownstream three-way catalyst has not yet had its excess oxygen reduced,the first cylinder group continues at a rich air-fuel ratio to reduceall the stored oxygen in the upstream three-way catalyst coupled to thefirst group, and therefore provide reductants to reduce some of thestored oxygen in the downstream three-way catalyst. Thus, at time T4,the rich operation of the first cylinder group has ended since thedownstream three-way catalyst has reached its desired amount of storedoxygen. However, at this point, since the upstream three-way catalyst issaturated at substantially no oxygen storage, the first cylinder groupsoperate slightly lean for a short duration until T5 to reestablish thestored oxygen in the upstream three-way catalyst. At time T5, then bothcylinder groups operate about stoichiometry until time T6, at which timeagain is desired to operate both cylinders without fuel injection. Thisoperation continues to time T7 at which point it is desired to re-enableonly one of the cylinder groups to carry out combustion. Thus, the firstcylinder group is operated at a rich air-fuel ratio for a short durationuntil the oxygen storage has been reestablished in the first upstreamthree-way catalyst coupled to the first cylinder group. Then, the firstcylinder group returns to stoichiometric operation until time T8. Attime T8, it is desired to re-enable the second cylinder group. At thistime, the second cylinder group operates at a rich air-fuel ratio thatvaries depending on the engine operating conditions to reestablish thestored oxygen in the downstream three-way catalyst. Then, at time T9,the second cylinder group operates slightly lean for a short duration toreestablish some stored oxygen in the upstream three-way catalystcoupled to the second group. Then, both cylinder groups are operated tooscillate above stoichiometry.

[0220] In this way, improved operation into and out of cylinder fuel cutconditions can be achieved.

[0221] Note that regarding the approach taken in FIG. 13 by re-enablingwith rich combustion, any NOx generated during the re-enablement can bereacted in the three way catalyst with the rich exhaust gas, furtherimproving emission control.

[0222] Referring now to FIGS. 14 and 15, example emission controlsdevice are described which can be used as devices 300 and/or 302 fromFIG. 2. As discussed above, fuel economy improvements can be realized onengines (for example, large displacement engines) by disabling cylindersunder conditions such as, for example, low load, or low torque requestconditions. Cylinder deactivation can take place by either deactivatingvalves so the cylinders do not intake or exhaust air or by deactivatingfuel injectors to the inactive cylinders pumping air. In the latterscheme, the bifurcated catalyst described in FIGS. 14 and 15 has theadvantage that they can keep the exhaust from the firing cylindersseparate from the non-firing cylinders so that the emission controldevice (such as, for example, a 3-way catalyst) can effectively convertthe emissions from the firing cylinders. This is true even when used onan uneven firing V8 engine (where disabling cylinders to still give atorque pulse every 180 crank angle degrees requires disabling half ofthe cylinders on one bank and half of the cylinders on the other bank).The bifurcated catalyst approach thus avoids the need to pipe the aircylinders to one catalyst and the firing cylinders to another catalystwith a long pipe to cross the flow from one side of the engine to theother. As such, it is possible, if desired, to maintain current catalystpackage space without requiring complicated crossover piping.

[0223] Specifically, FIG. 14 shows a bifurcated catalyst substrate 1410with a front face 1420 and a rear face (not shown). The substrate isdivided into an upper portion 1422 and a lower portion 1424. Thesubstrate is generally oval in cross-sectional shape; however, othershapes can be used, such as circular. Further, the substrate is formedwith a plurality of flow paths formed from a grid in the substrate. Inone particular example, the substrate is comprised of metal, which helpsheat conduction from one portion of the device to the other, therebyimproving the ability to operate one group of cylinders in a fuel-cutstate. However, a ceramic substrate can also be used.

[0224] The substrate is constructed with one or more washcoats appliedhaving catalytic components, such as ceria, platinum, palladium,rhodium, and/or other materials, such as precious metals (e.g., metalsfrom Group-8 of the periodic table). However, in one example, adifferent washcoat composition can be used on the upper portion of thesubstrate and the lower portion of the substrate, to accommodate thedifferent operating conditions that may be experienced between the twoportions. In other words, as discussed above, one or the other of theupper and lower portions can be coupled to cylinders that are pumpingair without injected fuel, at least during some conditions. Further, oneportion or the other may be heated from gasses in the other portion,such as during the above described cylinder fuel-cut operation. As such,the optimal catalyst washcoat for the two portions may be different.

[0225] In this example, the two portions are symmetrical. This may allowfor the situation where either group of cylinders coupled to therespective portions can be deactivated if desired. However, in analternative embodiment, the portions can be asymmetrical in terms ofvolume, size, length, washcoats, or density.

[0226] Referring now to FIG. 15, an emission control device 1510 isshown housing substrate 1410. The device is shown in this example withan inlet cone 1512 an inlet pipe 1514, an exit cone 1516, and an exitpipe 1618. The inlet pipe and inlet cone are split into two sides (shownhere as a top and bottom portion; however, any orientation can be used)each via dividing plates 1520 and 1522. The two sides may be adjacent,as shown in the figure, but neither portion encloses the other portion,in this example. The dividing plates keep a first and second exhaust gasflow stream (1530 and 1532) separated up to the point when the exhaustgas streams reach the substrate portions 1422 and 1424, respectively.The dividing plates are located so that a surface of the plate islocated parallel to the direction of flow, and perpendicular to a faceof the substrate 1410. Further, as discussed above, because the pathsthrough the substrate are separated from one another, the two exhaustgas streams stay separated through substrate 1410. Also, exit cone 1516can also have a dividing plate, so that the exhaust streams are mixedafter entering exit pipe 1518.

[0227] Continuing with FIG. 15, four exhaust gas oxygen sensors areillustrated (1540, 1542, 1544, and 1546), however only a subset of thesesensors can be used, if desired. As shown by FIG. 15, sensor 1540measures the oxygen concentration, which can be used to determine anindication of air-fuel ratio, of exhaust stream 1530 before it istreated by substrate 1410. Sensor 1542 measures the oxygen concentrationof exhaust stream 1532 before it is treated by substrate 1410. Sensor1544 measures the oxygen concentration of exhaust stream 1530 after itis treated by substrate 1410, but before it mixes with stream 1532.Likewise, sensor 1546 measures the oxygen concentration of exhauststream 1532 after it is treated by substrate 1410, but before it mixeswith stream 1530. Additional downstream sensors can also be used tomeasure the mixture oxygen concentration of streams 1530 and 1532, whichcan be formed in pipe 1518.

[0228]FIG. 15 also shows cut-away views of the device showing an ovalcross-section of the catalyst substrate, as well as the inlet and outletcones and pipes. However, circular cross-sectional pipe, as well assubstrate, can also be used.

[0229] Referring now to FIG. 16, a routine is described for selecting adesired idle speed control set-point for idle speed control which takesinto account whether cylinders are deactivated, or whether splitignition timing is utilized. Specifically, as shown in step 1610, theroutine determines a desired idle speed set-point, used for feedbackcontrol of idle speed via fuel and/or airflow adjustment, based on theexhaust temperature, time since engine start, and/or the cylinder cutstate. This allows for improved NVH control, and specifically provides,at least under some conditions, a different idle speed set-pointdepending on cylinder cut-operation to better consider vehicleresonances. The control strategy of desired idle rpm may also bemanipulated to improve the tolerance to an excitation type. For example,in split ignition mode, a higher rpm set-point may reduce NVH by movingthe excitation frequency away from that which the vehicle is receptive.Thus, the split ignition idle rpm may be higher than that of a non-splitignition mode.

[0230] Referring now to FIG. 17, a routine is described for coordinatingcylinder deactivation with diagnostics. Specifically, cylinderdeactivation is enabled and/or affected by a determination of whetherengine misfires have been identified in any of the engine cylinders.

[0231] For example, in the case of a V-6 engine as shown in FIG. 2F, ifit is determined that an ignition coil has degraded in one of thecylinders in group 250, then this information can be utilized inenabling, and selecting, cylinder deactivation. Specifically, if thecontrol routine alternatively selects between group 250 and 252 to bedeactivated, then the routine could modify this selection based on thedetermination of degradation of a cylinder in group 250 to selectcylinder deactivation of group 250 repeatedly. In other words, ratherthan having the ability to deactivate ether group 250 or group 252, theroutine could deactivate the group which has a cylinder identified asbeing degraded (and thus potentially permanently deactivated untilrepair). In this way, the routine could eliminate, at least under someconditions, the option of deactivating group 252. Otherwise, if group252 were selected to be deactivated, then potentially four out of sixcylinders would be deactivated, and reduced engine output may beexperienced by the vehicle operator.

[0232] Likewise, if diagnostics indicate that at least one cylinder fromeach of groups 250 and 252 should be disabled due to potential misfires,the cylinder cut-out operation is disabled, and all cylinders (exceptthose disabled due to potential misfires) are operated to carry outcombustion.

[0233] Thus, if the control system has the capability to operate on lessthan all the engine's cylinders and still produce driver demanded torquein a smooth fashion, then such a mode may be used to disable misfiringcylinders with minimal impact to the driver. This decision logic mayalso include the analysis of whether an injector cutout pattern wouldresult in all the required cylinders being disabled due to misfire.

[0234]FIG. 17 describes an example routine for carryout out thisoperation. Specifically, in step 1710, the routine determines whetherthe engine diagnostics have identified a cylinder or cylinders to havepotential misfire. In one example, when the diagnostic routines identifycylinder or cylinders to have a potential misfire condition, such as dueto degraded ignition coils, those identified cylinders are disabled andfuel to those cylinders is deactivated until serviced by a technician.This reduces potential unburned fuel with excess oxygen in the exhaustthat can generate excessive heat in the exhaust system and degradeemission control devices and/or other exhaust gas sensors.

[0235] When the answer to step 1710 is no, the routine ends.Alternatively, when the answer to step 1710 is yes, the routinecontinues to step 1712, where a determination is made as to whetherthere is a cylinder cutout pattern for improved fuel economy that alsosatisfies the diagnostic requirement that a certain cylinder, orcylinders, be disabled. In other words, in one example, the routinedetermines whether there is a cylinder cutout mode that can be used forfuel economy in which all of the remaining active cylinders are able tobe operated with fuel and air combusting. When the answer to step 1712is yes, the routine continues to step 1714 in which the patterns thatmeet the above criteria are available for injector cutout operation.Patterns of cylinder cutout in which cylinders that were selected toremain active have been identified to have potential misfire, aredisabled.

[0236] In this way, it is possible to modify the selection andenablement of cylinder cutout operation to improve fuel economy, whilestill allowing proper deactivation of cylinders due to potential enginemisfires.

[0237] As described in detail above, various fuel deactivationstrategies are described in which some, or all, of the cylinders areoperated in a fuel-cut state depending on a variety of conditions. Inone example, all or part of the cylinders can be operated in a fuel-cutstate to provide improved vehicle deceleration and fuel economy since itis possible to provide engine braking beyond closed throttle operation.In other words, for improved vehicle deceleration and improved fueleconomy, it may be desirable to turn the fuel to some or all of theengine cylinders engine off under appropriate conditions.

[0238] However, one issue that may be encountered is whether the enginespeed may drop too much after the fuel is disabled due to the drop inengine torque. Depending on the state of accessories on the engine, thestate of the torque converter, the state of the transmission, and otherfactors discussed below, the fuel-off torque can vary.

[0239] In one example, an approach can be used in which a thresholdengine speed can be used so that in worst case conditions, the resultingengine speed is greater than a minimum allowed engine speed. However, inan alternative embodiment, if desired, a method can be used thatcalculates, or predicts, the engine speed after turning off the fuel fora vehicle in the present operating conditions, and then uses thatpredicted speed to determine whether the resulting engine speed will beacceptable (e.g., above a minimum allowed speed for those conditions).For example, the method can include the information of whether thetorque converter is locked, or unlocked. When unlocked, a model of thetorque converter characteristics may be used in such predictions.Further, the method may use a minimum allowed engine speed to determinea minimum engine torque that will result from fuel shut off operation toenable/disable fuel shut off. Examples of such control logic aredescribed further below with regard to FIG. 18. Such a method could alsobe used to screen other control system decisions that will affectproduction of engine torque in deceleration conditions, such as whetherto enable/disable lean operation in cylinders that remain combustingwhen others are operated without fuel injection. Examples of suchcontrol logic are described further below with regard to FIG. 19.

[0240] Furthermore, such an approach can be useful during tip-outconditions in still other situations, other than utilizing full orpartial cylinder fuel deactivation, and other than enabling/disablingalternative control modes. Specifically, it can also be used to adjust arequested engine torque during deceleration conditions in which othertypes of transitions may occur, such as transmission gear shifts. Thisis described in further detail below with regard to FIGS. 20-21.

[0241] Referring now to FIG. 18, a model based screening (via a torqueconverter model, for example) for whether to enable (full or partial)fuel shut off operation to avoid excessive engine speed drop isdescribed. First, in step 1810, the routine determines whether thetorque converter is in the locked or partially locked condition. Thepartially locked condition can be encountered when the lock up clutch isbeing applied across the torque converter, yet has not fully coupled thetorque converter input and output. In one example, the determination ofstep 1810 is based upon whether the slip ratio between the input torqueconverter speed and the output torque converter speed is approximatelyone. When the answer to step 1810 is yes, the routine continues to step1822, as discussed in further detail below. When the answer to step 1810is no, the routine continues to step 1812. In step 1812, the routinecalculates the minimum allowed engine speed during a decelerationcondition. In one example, deceleration condition is indicated by adriver tipout of the accelerator pedal (i.e., an accelerator pedalposition less than a threshold value). The minimum allowed engine speedcalculated in step 1812 can be based on a variety of operatingconditions, or selected to be a single value. When the minimum allowedengine speed is dependent upon operating conditions, it can becalculated based on conditions such as, for example: vehicle speed,engine temperature, and exhaust gas temperature.

[0242] Continuing with FIG. 18, in step 1814, the routine predicts aturbine speed at a future interval using vehicle deceleration rate. Thisprediction can be preformed utilizing a simple first order rate ofchange model where the current turbine speed, and current rate ofchange, are used to project a turbine speed at a future instant based ona differential in time. Next, in step 1816, the routine calculates aminimum engine torque required to achieve the calculated minimum allowedengine speed with the predicted turbine speed. Specifically, the routineuses a model of the torque converter to calculate the minimum amount ofengine torque that would be necessary to maintain the engine speed atthe minimum allowed speed taking into account the predicted turbinespeed. The details of this calculation are described below with regardto FIG. 20.

[0243] Next, in step 1818, the routine calculates the maximum enginebrake torque available to be produced in a potential new control modethat is being considered to be used. For example, if the potential newcontrol mode utilizes cylinder cut operation, this calculation takesinto account that some or all of the cylinders may not be producingpositive engine torque. Alternatively, if the new control mode includeslean operation, then again the routine calculates the maximum enginebrake torque available taking into account the minimum available leanair fuel ratio.

[0244] Make a note that regarding step 1818, the first example isdescribed in more detail below with regard to FIG. 19.

[0245] Next, in step 1820, the routine determines whether the calculatedmaximum engine brake torque in the potential new control mode is greaterthan the engine torque required to achieve, or maintain, the minimumallowed engine speed. If the answer to step 1820 is yes, the routinecontinues to step 1822 to enable the new control mode based on thisengine speed criteria. Alternatively, when the answer to step 1820 isno, the routine continues to step 1824 to disable the transition to thenew control mode based on this engine speed criteria. In this way, it ispossible to enable or disable alternative control modes taking intoaccount their effect on maintaining a minimum acceptable engine speedduring the deceleration condition, and thereby reduce engine stalls.Make a note before the description of step 1810 that the routine to FIG.18 may be preformed during tipout deceleration conditions.

[0246] Referring now to FIG. 19, the routine of FIG. 18 has beenmodified to specifically apply to the cylinder fuel cut operatingscenario. Steps 1910-1916 are similar to those described in steps1810-1816.

[0247] From step 1916, the routine continues to step 1918 where theroutine calculates the engine brake torque that will result from turningoff fuel at the minimum engine speed. Specifically, the routinecalculates the engine brake torque that will be produced after turningfuel injection off to part or all of the cylinders. Further, thiscalculation of brake torque is preformed at the minimum engine speed.Then, in stop 1920, the routine determines whether this resulting enginetorque at the minimum engine speed during fuel cut operation is greaterthen the engine torque required to achieve, or maintain, the minimumallowed engine speed. If so, then the engine torque is sufficient in thefuel cut operation, and therefore the fuel cut operation is enabledbased on this engine speed criteria in step 1922. Alternatively, whenthe answer to step 1920 is no, then the engine torque that can beproduced in the full or partial fuel cut operation at the minimum enginespeed is insufficient to maintain the minimum engine speed, andtherefore the fuel shut-off mode is disable based on this engine speedcriteria. In this way, it is possible to selectively enable/disable fulland/or partial fuel deactivation to the cylinders in a way thatmaintains engine speed at a minimum allowed engine speed. In this way,engine stalls can be reduced.

[0248] Note that in this way, at least under some conditions, it ispossible to enable (or continue to perform) fuel deactivation to atleast one cylinder at a lower engine speed when the torque converter islocked than when the torque converter is unlocked. Thus, fuel economycan be improved under some conditions, without increasing occurrence ofengine stalls.

[0249] Referring now to FIGS. 20 and 21, a routine is described forclipping a desired engine torque request to maintain engine speed at orabove a minimum allowed engine speed during vehicle tip-out conditionsutilizing torque converter characteristics. In this way, it is possibleto reduce dips in engine speed that may reduce customer feel.

[0250] For example, in calibrating a requested impeller torque as afunction of vehicle speed for one or more of the engine braking modes,it is desirable to select torque values that give good engine brakingfeel and are robust in the variety of operating conditions. However,this can be difficult since a variety of factors affect engine braking,and such variations can affect the resulting engine speed. Specifically,it can be desirable to produce less than the required torque to idleunder deceleration conditions to provide a desired decelerationtrajectory. However, at the same time, engine speed should be maintainedabove a minimum allowed engine speed to reduce stall. In other words,one way to improve the system efficiency (and reduce run-on feel) underdeceleration conditions is to produce less engine torque than needed toidle the engine. Yet at the same time, engine speed drops should bereduced that let engine speed fall below a minimum allowed value.

[0251] In one example, for vehicles with torque converters, a model ofthe open torque converter can be used to determine the engine torquethat would correspond to a given engine speed (target speed or limitspeed), and thus used to allow lower engine torques during deceleration,yet maintain engine speed above a minimum value. In this case, if thereis a minimum allowed engine speed during deceleration, the controllercan calculate the engine torque required to achieve at least thatminimum engine speed based on turbine speed. The routine below uses two2-dimensional functions (fn_conv_cpc and fn_conv_tr) to approximate theK-factor and torque ratio across the torque converter as a function ofspeed ratio. This approximation includes coasting operation where theturbine is driving the impeller. In an alternative approach, moreadvanced approximations can be used to provide increased accuracy, ifnecessary.

[0252] Note that it is known to use a model of the open torque converterto determine the engine torque that would correspond to a given enginespeed in shift scheduling for preventing powertrain hunting. I.e., it isknown to forecast the engine speed (and torque converter output speed)after a shift to determine whether the engine can produce enough torqueto maintain tractive effort after an upshift (or downshift) in thefuture conditions. Thus, during normal driving, it is known to screenshift requests to reduce or prevent less than equal horsepower shifts(including a reserve requirement factor), except for accelerations.Further, it is known to include cases where the torque converter islocked, and to include calculations of maximum available engine torque.

[0253] Referring now to FIG. 20, a routine is described for calculatingthe engine brake torque required to spin the engine at a specifiedengine speed and turbine speed. First, in step 2010, temporaryparameters are initialized. Specifically, the following 32-bit variablesare set to zero: tq_imp_ft_lbf_tmp (temporary value of impeller torquein lbf), tq_imp_Nm_tmp (temporary value of impeller torque in Nm),cpc_tmp (temporary value of K-factor), and tr_tmp (temporary value oftorque ratio). Further, the temporary value of the speed ratio(speed_ratio_tmp)=is calculated as a ratio of the temporary turbinespeed (nt_tmp) and the temporary engine speed (ne_tmp), clipped to 1 toreduce noise in the signals.

[0254] Then, in step 2012, the routine calculates the temporary K-factor(cpc_tmp) as a function of the speed ratio and converter characteristicsstored in memory using a look-up function, for example. Then, in step2014, a determination is made as to whether the speed ratio (e.g.,speed_ratio_tmp>1.0 ?). If so, this signifies that the vehicle iscoasting, and positive engine torque is not being transmitted throughthe torque converter. When the answer to step 2014 is Yes, the routinecontinues to step 2016. In step 2016, the routine uses a K-factorequation that uses turbine speed and torque as inputs. Specifically, theimpeller torque is calculated from the following equations:

tq _(—) imp _(—) ft _(—) lbf _(—) tmp=nt _(—) tmp*nt _(—) tmp/max((cpc_(—) tmp* cpc _(—) tmp), 10000.0);

tr _(—) tmp=f(speed _(—) ratio _(—) tmp);

tq _(—) imp _(—) ft _(—) lbf _(—) tmp=−tq _(—) imp _(—) ft _(—) lbf _(—)tmp/tr _(—) tmp;

[0255] where the function f stores data about the torque converter togenerate the torque ratio (tr) based on the speed ratio.

[0256] Otherwise, when the answer to step 2014 is No, then the K-factorequation uses engine speed and torque as inputs, and the routinecontinues to step 2018. In step 2018, the impeller torque is calculatedfrom the following equations:

tq _(—) imp _(—) ft _(—) lbf _(—) tmp=ne _(—) tmp*ne _(—) tmp/max((cpc_(—) tmp* cpc _(—) tmp), 10000.0)

[0257] Then, these can be converted to NM units, and losses included,via the following equation in step 2020.

tq _(—) imp _(—) Nm _(—) tmp=tq _(—) imp _(—) ft _(—) lbf _(—)tmp*1.3558+tq _(—) los _(—) pmp;

[0258] In this way, it is possible to calculate a required torque(tq_imp_Nm_tmp) to maintain engine speed as desired. Example operationis illustrated in FIG. 21. Specifically, FIG. 21 demonstrates theperformance of this torque request clipping/screening during vehicletesting. At approximately 105.5 seconds the accelerator pedal isreleased and the torque based deceleration state machine enters holdsmall positive mode (where a small positive torque is maintained on thedrivetrain) followed by an open loop braking mode, where negative enginetorque is provided in an open-loop fashion. Soon after the tip-out, thetransmission controls command a 3-4 up-shift which will lower theturbine speed below the minimum engine speed target of ˜850 rpm in thisexample, placing a torque load on the engine. This transmission up-shiftmay result in more engine torque being required to hold 850 rpm enginespeed and tqe_decel_req_min (the lower clip applied to the tqe_decel_reqvalue) therefore jumps to 42 Nm to reflect the higher torque request.The value of tqe_decel_req_min is calculated based on the torqueconverter model described above. By keeping the deceleration torquerequest from dropping too low, the engine speed behaves as desired.

[0259] Referring now to FIGS. 22-27, a method for managing the cycleaveraged torque during transitions between different cylinder cut-outmodes is described. Specifically, such an approach may provide improvedtorque control during these transitions. Before describing the controlroutine in detail, the following description and graphs illustrate anexample situation in which it is possible to better control cycleaveraged torque during the transition (note that this is just oneexample situation in which the method can be used). These graphs use theexample of an eight cylinder engine where the cylinders on the engineare numbered in firing order. When the system transitions from firing 1,3, 5, 7 to 2, 4, 6, 8, for example, two cylinders may fire insuccession. If the torque produced by all the cylinders during thetransition is substantially the same, the cycle-average torque producedduring the transition may be higher than desired, even though no onecylinder produces substantially more or less torque, and over a cycle,the same number of cylinders is still being fired. In other words, thereis a single, effective shift of half of the cylinders firing earlier inthe overall engine cycle. This torque disturbance may also result in anengine speed disturbance if occurring during idle speed controlconditions. The following figures illustrate an example of this torquedisturbance.

[0260] Note that the following description illustrates a simplifiedexample, and is not meant to define operation of the system.

[0261]FIG. 22 shows the crankshaft torque for an 8 cylinder engine withall cylinders firing, where the crankshaft torque resulting from the sumof the power strokes on the engine are modeled as simple sine waves. Forthe example where four cylinders are operated to produce the same nettorque as all 8 in FIG. 22, then the torque production of each cylinderwould double as shown in FIG. 23.

[0262] If this same level of torque was produced by the firing cylindersin 4 cylinder mode but the system transitioned from firing 1-3-5-7 to2-4-6-8 with the last cylinder fired before the transition being 3 andthe first cylinder fired after the transition being 4, then crankshafttorque would be as illustrated in FIG. 24. As shown in FIG. 24, thesumming of the torques from cylinders 3 and 4 may produce a torqueincrease during this transition point and an increase in the averagetorque over an engine cycle. The increase could be as much as 12.5% foran 8 cylinder engine, or 16.7% for a 6 cylinder engine due to thisoverlapping torque addition effect. By recognizing this behavior, thecontrol system can be redesigned to reduce the torque produced by theoff-going cylinder (3 in this example) and the on-coming cylinder (4 inthis example) such that the average torque over a cycle is not increasedduring a transition.

[0263] For an 8 cylinder engine, if the torque produced by cylinders 3and 4 were reduced by approximately 25% each, then the torque profilewould resemble FIG. 25, with the cycle average torque approximatelymatching the steady 4 or 8 cylinder operation.

[0264] In this way, it is possible to improve torque control whentransitioning between operating in a first mode with the first groupcombusting inducted air and injected fuel and the second group operatingwith inducted air and substantially no injected fuel, and operation in asecond mode with the second group combusting inducted air and injectedfuel and the first group operating with inducted air and substantiallyno injected fuel. As indicated in the example, above, before thetransition, engine torque of a last to be combusted cylinder in thefirst group is reduced compared with a previously combusted cylinder inthat group. Further, after the transition, engine torque of a first tobe combusted cylinder in the second group is reduced compared with anext combusted cylinder in that group.

[0265] The reduction of one or both of the cylinder can be accomplishedin a variety of ways, such as, for example: ignition timing retard, orenleanment of the combusted air and fuel mixture. Further, usingelectric valve actuation, variable valve lift, an electronic throttlevalve, etc., the reduction could be performed by reducing air charge inthe cylinders.

[0266] In an alternative embodiment, it may be possible to provideimprove torque control during the transition by reducing torque of onlyone of the last to be fired cylinder in the first group and the first tobe fired cylinder in the second group. Further, it may be possible toprovide improve torque control during the transition by providingunequal torque reduction in both the last to be fired cylinder in thefirst group and the first to be fired cylinder in the second group.

[0267] For example, the torque reduction for the last cylinder of theold firing order (in the example discussed above, cylinder 3) and thefirst cylinder of the new firing order (cylinder 4) could be implementedin any way such that the total indicated torque produced by these twocylinders was reduced by approximately 25%. For example, if the torquereduction of the last cylinder in the firing order is X*50% and thereduction of the first cylinder in the new firing order is (1−X)*50%,average torque could be maintained. For the example reduction of 25%each, X=0.5.

[0268] If all the torque were reduced on the last old firing ordercylinder (X=1), the results would be similar to those shown in FIG. 26.Alternatively, if all the torque reduction was accomplished with thefirst cylinder of the new firing order (X=0), then the results would besimilar to those shown in FIG. 27. These are just two example, and Xcould be selected anywhere between 0 and 1.

[0269] Referring now to FIGS. 28-33, an approach to reduce engine NVHduring mode transitions between full cylinder operation and partialcylinder operation (between full cylinder operation and split ignitiontiming operation).

[0270]FIG. 28 shows the frequency content of the engine at 600 RPM withall cylinders firing at stoichiometry and optimal ignition timing. Thefigure shows a dominant peak at firing frequency of all cylinders firing(FF). This can be compared with FIG. 29, which shows the frequencycontent of the engine at 600 RPM operating in cylinder cut out mode(e.g., fuel to one bank of a V-6 deactivated, or fuel to two cylinderson each bank of a V-8 deactivated), or operating with split ignitiontiming between groups of cylinders. This shows a dominant peak at ½ FF,and a smaller peak at firing frequency due to compression of allcylinders, since deactivated cylinders still pump air. And both FIGS. 28and 29 can be compared with FIG. 30, which shows the frequency contentof the engine at 600 RPM with all cylinders firing at a lean air-fuelratio and/or with regarded ignition timing. FIG. 30 shows a dominantpeak at FF, but with a wider spread due to increased combustionvariability due to lean, and/or retarded ignition timing.

[0271] When abruptly transitioning between these modes, there may be abroad band excitation due to the change in fundamental frequency contentof the engine torque. This may excite resonance frequencies of thevehicle, such as a vehicle's body resonance, as shown by FIG. 31.Therefore, in one example when such NVH concerns are present, the enginecan be operated to gradually make the transition (e.g., by graduallyreducing torque in combusting cylinders and gradually increasing torquein deactivated cylinders when enabling combustion in deactivatedcylinders). For example, this can be performed via split airflow controlbetween the cylinder groups. Alternative, enleanment and/or ignitiontiming retard can also be used. In this way, the frequency excitation ofany vehicle frequencies may be reduced. In other words, ramping to andfrom different modes may allow jumping over body resonances so thatinjector cut-out (or split ignition timing) can operate at lower enginespeeds (e.g., during idle) while reducing vibration that may be causedby crossing and excite a body resonance. This is discussed in moredetail below with regard to FIGS. 32-33.

[0272] Specifically, FIG. 32 shows the frequency content at a mid-pointof a transition in which there are two smaller, broader peaks centeredabout FF and ½ FF. In this example, the engine transitions fromoperating with split ignition timing to operating all cylinders withsubstantially the same ignition timing. For example, the controllerreduces airflow, or retards ignition timing, or enleans, cylindersgenerating power, and advanced ignition timing of the cylinders withsignificant ignition timing retard. FIG. 33 shows the frequency contentnear the end of the transition when all of the cylinders are carryingout combustion at substantially the same, retarded, ignition timing.

[0273] Thus, by using ramping, it may be possible to operate at a loweridle rpm by reducing potential NVH consequence and gradually changingtorque frequency content, rather than abruptly stepping to and fromdifferent modes with the resultant broad band excitation due tofrequency impulses. Further, this may be preferable to an approach thatchanges engine speed through a resonance before making a transition,which may increase NVH associated with running at a body resonancefrequency.

[0274] Note that these figures show a single body resonance, however,there could also be drive line or mount resonances that vary withvehicle speed and gear ratio.

[0275] Referring now to FIG. 34, an example control strategy isdescribed for use with a system such as in FIG. 2Q, for example. Thisstrategy could be used with any even fire V-type engine such as, forexample: a V-6 engine, a V-10 engine, a V-12 engine, etc. Specifically,this strategy uses a stoichiometric injector cut-out operation where onegroup of cylinders is operated to induct air with substantially no fuelinjection, and the remaining cylinders are operating to combust a nearstoichiometric air-fuel mixture. In this case, such as in the example ofFIG. 2Q, catalysts 222 and 224 can be three-way type catalysts. Alsonote that a third catalyst can be coupled further downstream in anunderbody location, which can also be a three-way catalyst. In this way,it is possible to disable the cylinder group without an upstreamthree-way catalyst (e.g., group 250), while continuing to operate theother group (group 252) in a stoichiometric condition. In this way,catalyst 222 can effectively reduce exhaust emissions from group 252.Further, when both groups are combusting a stoichiometric mixture, bothcatalysts 222 and 224 (as well as any further downstream catalysts) canbe used to effectively purify exhaust emissions.

[0276] This exhaust system has a further advantage in that it is able toimprove maintenance of catalyst temperatures even in the injectorcut-out mode. Specifically, during cylinder fuel injection cut-out,catalyst 222 can convert emissions (e.g. HC, CO and NOx) in thestoichiometric exhaust gas mixture (which can oscillate aboutstoichiometry). The relatively cool air from bank 250 mixes with the hotstoichiometric exhaust gases before being fed to catalyst 224. However,this mixture is approximately the same temperature in the fuel injectioncut-out mode as it would be in stoichiometric operation where bothcylinders 250 and 252 carry out combustion. Specifically, when in theinjector cut-out mode, the stoichiometric cylinder load is approximatelytwice the exhaust temperature in the mode of both groups carrying outcombustion. This raises the exhaust temperature coming out of thecylinders in group 252 to nearly twice that of the cylinders carryingout combustion at an equivalent engine load. Thus, when excess air isadded to the hotter exhaust gas in the cylinder cut-out mode, theoverall temperature is high enough to keep catalysts 224 in a light-offmode. Therefore, when the engine exits the injector cut-out mode, bothcatalysts 222 and 224 are in a light-off mode and can be used to reduceemissions.

[0277] If, however, the exhaust system design is such that in theinjector cut-out mode catalyst 224 still cools below a desired catalysttemperature, then split ignition operation can be used when re-enablingcombustion to both cylinder groups as described above with regard toFIG. 8. Specifically, when transitioning from operating with group 250in the cylinder in the fuel cut mode, and group 252 operating aboutstoichiometry—to operating both groups about stoichiometry, group 250can be re-enabled with fuel injection to carry out combustion with asignificantly retarded ignition timing. In this way, catalysts 224 canbe rapidly heated due to the large amount of heat generated by group250. Further, the significantly less retarded combustion of group 252maintains the engine output smoothly about a desired value.

[0278] As described above, the configuration of FIG. 2Q can providesignificant advantages in the fuel cut mode, however, the inventorsherein have recognized that during cold starting conditions, catalyst224 reaches a light off temperature slower than catalyst 222 due to thefurther distance from cylinder Group 250 and being in the downstreamposition relative to catalyst 222. Therefore, in one example, it ispossible to provide better catalyst light off operation during a startusing the split ignition timing approach described above herein. This isdescribed in further detail below with regard to FIG. 34.

[0279] Referring now specifically to FIG. 34, a routine as describedbefore regarding engine starting operation with an unequal exhaust pathto the first catalyst such as in the system of FIG. 2Q, for example.First, in step 3410, the routine determines whether the exhaustconfiguration is one having unequal exhaust paths to a first catalyst.If the answer to step 3410 is “yes”, the routine continues to step 3412.In step 3412, the routine determines whether the current conditions area “cold engine start.” This can be determined based on a time-sensitivelast engine operation, engine coolant temperature and/or various otherparameters. If the answer to step 3412 is “yes”, the routine continuesto step 3414 to operate the engine in a crank mode.

[0280] In the crank mode, the engine starter rotates the engine up to aspeed at which it is possible to identify cylinder position. At thispoint, the engine provides for fuel injection to all the cylinders in asequential mode, or in a “big bang” mode. In other words, the routinesequentially provides fuel injection to each of the engine cylinders inthe desired fire mode to start the engine. Alternatively, the routinefires off fuel injectors simultaneously to all the cylinders andsequentially fires the ignition into each cylinder in the firing orderto start the engine.

[0281] The routine then continues to step 3416 as the engine runs up tothe desired idle speed. During the run-up mode, it is possible again tooperate all of the cylinders to carry out combustion to run the engineup to a desired engine idle speed. At this point, the routine continuesto step 3418, where the power-heat mode (e.g., split ignition timing) isused. In this mode, the cylinder group coupled to an upstream emissioncontrol device (e.g., Group 252) is operated with potentially a slightlylean air-fuel mixture, and slightly retarded ignition timing frommaximum torque timing to maintain the cylinders at a desired enginespeed. However, the other group (Group 250) is then operated withsignificant ignition timing retard to produce little engine torqueoutput that provide significant amount of heat. While this combustionmay be past the combustion stability limit, smooth engine operation canbe maintained via the combustion in Group 252. The large amount of heatfrom Group 250 thereby quickly brings catalysts in the downstreamposition past a Y-pipe (e.g., catalyst 224) to a desired light-offtemperature. In this way, both catalysts can be rapidly brought to adesired temperature, at which the engine can transition to operatingboth cylinder groups with substantially the same ignition timing.

[0282] Note that in an alternative embodiment, the split ignition timingbetween the cylinder groups can be commenced during the run-up mode oreven during engine cranking.

[0283] It will be appreciated that the configurations and routinesdisclosed herein are exemplary in nature, and that these specificembodiments are not to be considered in a limiting sense, becausenumerous variations are possible. The subject matter of the presentdisclosure includes all novel and nonobvious combinations andsubcombinations of the various system and exhaust configurations, fuelvapor purging estimate algorithms, and other features, functions, and/orproperties disclosed herein. The following claims particularly point outcertain combinations and subcombinations regarded as novel andnonobvious. These claims may refer to “an” element or “a first” elementor the equivalent thereof. Such claims should be understood to includeincorporation of one or more such elements, neither requiring norexcluding two or more such elements. Other combinations andsubcombinations of the disclosed features, functions, elements, and/orproperties may be claimed through amendment of the present claims orthrough presentation of new claims in this or a related application.Such claims, whether broader, narrower, equal, or different in scope tothe original claims, also are regarded as included within the subjectmatter of the present disclosure.

We claim:
 1. A method for controlling an engine with at least a firstset of cylinders and a second set of cylinders, the method comprising:during an engine start, operating the second set of cylinders with anignition timing more retarded than an ignition timing of said first setof cylinders, and during engine operation, operating the first set ofcylinders with injected fuel to carry out combustion and operating thesecond set of cylinders to induct air and without injected fuel.
 2. Themethod of claim 1 where a first catalyst is coupled to the first set ofcylinders and a second catalyst is coupled to both said first and secondset of cylinders downstream of said first catalyst.
 3. The method ofclaim 2 wherein there is no catalyst coupled between said second set ofcylinders and said second catalyst.
 4. The method of claim 3 wherein athird catalyst is coupled downstream of said second catalyst.
 5. Themethod of claim 1 wherein during said engine start, the second set ofcylinders is operated with an ignition timing beyond a combustionstability limit.
 6. The method of claim 1 wherein during said enginestart, the second set of cylinders is operated with an ignition timingthat is retarded such that the second set of cylinders producesubstantially less torque per cylinder than produced by said first setof cylinder.
 7. The method of claim 1 wherein during engine operation,the first set of cylinders is operated with injected fuel to carry outcombustion about stoichiometry.
 8. The method of claim 7 wherein theengine is a V-6 engine.
 9. The method of claim 7 wherein the engine is aV-10 engine.
 10. The method of claim 7 wherein the engine is a V-12engine.
 11. The method of claim 7 wherein the engine is a V-6 engine,where said first set of cylinders is one bank of the V-engine, and saidsecond set of cylinders is the other bank of the V-engine.
 12. Themethod of claim 7 wherein the engine is a V-10 engine, where said firstset of cylinders is one bank of the V-engine, and said second set ofcylinders is the other bank of the V-engine.
 13. The method of claim 7wherein the engine is a V-12 engine, where said first set of cylindersis one bank of the V-engine, and said second set of cylinders is theother bank of the V-engine.
 14. A method for controlling an engine withat least a first set of cylinders and a second set of cylinders, where afirst catalyst is coupled to the first set and a second catalyst iscoupled to both said first and second set downstream of said firstcatalyst, the method comprising: operating the first set of cylinderswith injected fuel to carry out combustion and operating the second setof cylinders to induct air and without injected fuel; and after saidoperation, commencing fuel injection in said second set of cylinders,and during said commencing, operating said second set of cylinders withan ignition timing that is more retarded than an ignition timing of saidfirst set, with said first set carrying out combustion aboutstoichiometry.
 15. The method of claim 15 wherein there is no catalystcoupled between said second set of cylinders and said second catalyst.16. The method of claim 15 wherein a third catalyst is coupleddownstream of said second catalyst.
 17. The method of claim 1 whereinduring said commencing, the second set of cylinders is operated with anignition timing that is retarded such that the second set of cylindersproduce substantially less torque per cylinder than produced by saidfirst set of cylinder, yet produce more heat per cylinder than saidfirst set of cylinders.
 18. The method of claim 14 wherein the engine isa V-6 engine.
 19. The method of claim 14 wherein the engine is a V-10engine.
 20. The method of claim 14 wherein the engine is a V-12 engine.21. A computer readable storage medium having instructions encodedtherein for controlling an engine with at least a first set of cylindersand a second set of cylinders, the medium comprising: code for operatingthe second set of cylinders with an ignition timing more retarded thanan ignition timing of said first set of cylinders during an enginestart, and code for operating the first set of cylinders with injectedfuel to carry out combustion and operating the second set of cylindersto induct air and without injected fuel during subsequent engineoperation.